Predictive encoding and data decoding control

ABSTRACT

A shortest cut duration is a minimum required period between an edit point set on a stream of pictures such as an MPEG stream and the next edit point set on the stream. It is an object of the present invention to make restrictions on the shortest cut duration lenient in a process to seamlessly reproduce a result of editing the stream in order to enhance the freedom of editing in carrying out a process of editing the stream. In order to achieve this object, a controller detects each edit point set on the stream and, for the edit point, the controller identifies fewest possible pictures, which are not to be displayed but must be decoded first before decoding a picture to be displayed after the edit point. Then, the controller finds a start point representing a timing to start a process of decoding the one or fewest possible pictures. Subsequently, the controller controls processes carried out by decoders to decode the stream in picture units on the basis of the start point, and controls a switcher to select one of outputs of the decoders on the basis of the edit point.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to decoding control for enhancingthe freedom of a process to edit a moving picture.

[0002] An MPEG (Moving Picture Expert Group) technique is known as atypical method for compressing a moving picture, that is, for reducingthe amount of data representing the moving picture, by carrying out apredictive encoding process on any specific one of frames, which composethe moving picture, with reference to frames other than the specificone.

[0003] In accordance with the MPEG technique, data is subjected toquantization processing in an encoding process and encoded data issubjected to inversequantization processing in a decoding process. Thus,if the encoding and decoding processes are carried out repeatedly, thequality of a picture obtained as a result of the last decoding processis poor.

[0004] In order to solve this problem, in an operation to edit a movingpicture, which has been obtained as a result of an MPEG encodingprocess, the so-called edit points are set on an MPEG stream (or encodeddata), which serves as an editing raw material representing the movingpicture, without decoding the MPEG stream. The edit points are IN pointsand OUT points. Then, a list of edit points set on the MPEG stream ismade. The list is referred to hereafter as an edit-point list. In anoperation to reproduce a result of the editing operation, the MPEGstream is decoded in accordance with edit points shown on the edit-pointlist.

[0005] The aforementioned MPEG stream comprises GOPs each including aplurality of pictures. Symbol GOP (m) denotes an mth GOP as counted fromthe beginning of the MPEG stream. Assume for example that a startsequence of GOPs beginning with GOPi not shown in the figure and endingwith GOP (m) on an MPEG stream 201 shown in FIG. 1 has been reproduced.Then, GOP (n) located after GOP (m) is reproduced. Finally, anothersequence of GOPs beginning with GOP (m+2) located before GOP (n) andending with GOPj not shown in the figure is reproduced. The operationsto reproduce the start sequence, GOP (n) and the other sequence isreferred to as reproduction processing based on the so-called cutediting process. In this cut editing process, an edit-point list 202shown in FIG. 1 is made. It is to be noted that the edit-point list 202is shown only in a conceptual manner focusing on edit points. Details ofthe edit-point list 202 will be explained later.

[0006] In the edit-point list 202 shown in FIG. 1, an edit point T_(i)represents the start position of GOPi, which is reproduced as the firstGOP. The edit point T_(i) represents the end position of GOP (m) or thestart position of GOP (m+1). By the same token, an edit point T₂represents the end position of GOP (m+1) or the start position of GOP(m+2). In the same way, an edit point T₃ represents the end position ofGOP (n−1) or the start position of GOP (n). Similarly, an edit point T₄represents the end position of GOP (n) or the start position of GOP(n+1). In addition, an edit point Tj represents the start position ofGOPj, which is reproduced as the last GOP. It is to be noted that theedit points T_(1 and T) ₄ are each an OUT point while the edit points T₂and T₃ are each an IN point.

[0007] Notation ‘T_(i)→T_(l)’ on the first line of the edit-point list202 shown in FIG. 1 indicates that the MPEG stream 201 is to bereproduced from the position (time code) T₁ on the MPEG stream 201 tothe time code T₁. By the same token, notation ‘T₃ T₄’ on the second lineindicates that the MPEG stream 201 is to be reproduced the time code T₃to the time code T₄. In the same way, notation ‘T₂→T_(j)’ on the thirdline indicates that the MPEG stream 201 is to be reproduced the timecode T₂ to the time code T_(j).

[0008] Thus, in accordance with the edit-point list 202 shown in FIG. 1,the start sequence of GOPs beginning with GOPi and ending with GOP (m)on an MPEG stream 201 shown in FIG. 1 is first reproduced. Then, GOP (n)located after GOP (m+2) and GOPj is reproduced. Finally, the othersequence of GOPs beginning with GOP (m+2) and ending with GOPj isreproduced.

[0009] As described above, the edit-point list 202 is first made in anediting operation and the MPEG stream 201 is then reproduced in areproduction operation. Thus, by carrying out an editing operationwithout decoding the MPEG stream 201, it is possible to implement adesired editing operation and, hence, obtain a desired result ofediting.

[0010]FIG. 1 is a diagram showing an operation to edit only one MPEGstream as a raw editing material. It is to be noted, however, that aplurality of MPEG streams can also be used as a raw editing material tobe edited in the same way as that shown in FIG. 1.

[0011] By the way, in an operation to reproduce an MPEG stream, which isobtained as a result to edit a raw MPEG stream by making an edit-pointlist as described above, it is necessary to decode the resulting MPEGstream, that is, to put the resulting MPEG stream in an MPEG decodingprocess. Assume that an MPEG decoder for decoding the MPEG stream has adecoding-process speed by one. In this case, by using only a unit ofMPEG decoder having such a speed, it will be difficult to seamlesslyreproduce an MPEG stream, which is obtained as a result of a process toedit a raw MPEG stream by making an edit-point list as described above.

[0012] In accordance with the MPEG technique, there are provided threepicture types, namely, an Intra (I) picture, a Predictive (P) pictureand a Bidirectionally predictive (B) picture. An I picture is a pictureto be subjected to an intra encoding process without referencing otherpictures. A P picture is a picture to be subjected to an intra encodingprocess or a predictive encoding process, which is an encoding processcarried out by referencing an I picture or another P picture and using apredicted picture generated from the referenced picture. The referencedpicture is a picture displayed at a time preceding the P picture beingprocessed. A B picture is a picture to be subjected to an intra encodingprocess or a bidirectionally predictive encoding process, which is anencoding process carried out by referencing an I picture or another Ppicture and using a predicted picture generated from the referencedpicture. The referenced picture in the bidirectionally predictiveencoding process is a picture displayed at a time preceding orsucceeding the P picture being processed. It is to be noted that, whilean I or P picture can be used as a picture to be referenced in apredictive encoding process or a bidirectionally predictive encodingprocess, a B picture is never used as a picture to be referenced in anyencoding process.

[0013] As an example, consider a long GOP with a structure consisting of15 pictures (or 15 frames) wherein each of I and P pictures is placed asthe last one of three consecutive pictures including two other Bpictures.

[0014] Let alphabetical characters I, P and B denote respectively the I,P and B picture types of the pictures composing a GOP. In this case, anexample of a GOP is represented by a list as follows:

[0015] B1, B2, I3, B4, B5, P6, B7, B8, P9, B10, B11, P12, B13, B14, P15where a numerical subscript appended to each of the alphabeticalcharacters I, P and B denotes an order number of an order along the timeaxis.

[0016] As described above, a B picture is a picture encoded byreferencing not only a picture displayed at a time preceding the Bpicture, but also a picture displayed at a time succeeding the Bpicture. Thus, a B picture cannot be decoded unless the picture used asa referenced picture to be displayed at a time succeeding the B pictureis decoded before the B picture in a decoding operation.

[0017] In accordance with the MPEG technique, a picture used as areferenced picture in an operation to encode a B picture is encodedbefore the B picture. By the same token, a picture used as a referencedpicture in an operation to decode B picture is decoded before the Bpicture. In the case of the aforementioned list representing the GOPconsisting of pictures ranging from B1 to P15, the pictures are encodedand decoded in the following order:

[0018] I3, B1, B2, P6, B4, B5, P9, B7, B8, P12, B10, B11, P15, B13, B14.

[0019] To put it in detail, pictures B1 and B2 are each encoded anddecoded by referencing picture P15 displayed at a preceding time andpicture I3 displayed at a succeeding time. Picture P15 is a picturepertaining to the immediately preceding GOP while picture I3 is apicture pertaining to the same GOP.

[0020] Picture I3 is encoded and decoded without referencing anotherpicture.

[0021] Pictures B4 and B5 are each encoded and decoded by referencingpicture I3 displayed at a preceding time and picture P6 displayed at asucceeding time. Pictures I3 and P6 are each a picture pertaining to thesame GOP.

[0022] Picture P6 is encoded and decoded by referencing picture I3displayed at a preceding time. Picture I3 is a picture pertaining to thesame GOP.

[0023] Pictures B7 and B8 are each encoded and decoded by referencingpicture P6 displayed at a preceding time and picture P9 displayed at asucceeding time. Pictures P6 and P9 are each a picture pertaining to thesame GOP.

[0024] Picture P9 is encoded and decoded by referencing picture P6displayed at a preceding time. Picture P6 is a picture pertaining to thesame GOP.

[0025] Pictures B10 and B11 are each encoded and decoded by referencingpicture P9 displayed at a preceding time and picture P12 displayed at asucceeding time. Pictures P9 and P12 are each a picture pertaining tothe same GOP.

[0026] Picture P12 is encoded and decoded by referencing picture P9displayed at a preceding time. Picture P9 is a picture pertaining to thesame GOP.

[0027] Pictures B13 and B14 are each encoded and decoded by referencingpicture P12 displayed at a preceding time and picture P15 displayed at asucceeding time. Pictures P12 and P15 are each a picture pertaining tothe same GOP.

[0028] Picture P15 is encoded and decoded by referencing picture P12displayed at a preceding time. Picture P12 is a picture pertaining tothe same GOP.

[0029] As described above, pictures B1 and B2 of any GOP (n) are encodedand decoded by referencing an I or P picture displayed at a succeedingtime and an I or P picture displayed at a preceding time. In this case,the picture displayed at the succeeding time is picture I3 pertaining tothe same GOP (n) but the picture displayed at the preceding time ispicture P15 pertaining to GOP (n−1) immediately preceding GOP (n).

[0030] Assume that the current edit point is set at the head of GOP (n).In this case, in order to carry out a reproduction process starting fromthe head of GOP (n), GOP (n) cannot be decoded unless GOP (n−1)immediately preceding GOP (n) is decoded first as is obvious from apicture-decoding order 203 shown in FIG. 2.

[0031] To put it concretely, in order to decode pictures B1 and B2pertaining to GOP (n), it is necessary to reference picture P15 of GOP(n−1) immediately preceding GOP (n). In accordance with the conventionaltechnology, an MPEG decoder is controlled in GOP units so that GOP (n)cannot be decoded unless GOP (n−1) immediately preceding GOP (n) isdecoded first.

[0032] In accordance with the conventional technology, only the picturescomposing GOP (n) are displayed without displaying the picturescomposing GOP (n−1) as is obvious from a picture-decoding order 204shown in FIG. 2 in spite of the fact that both GOP (n) and GOP (n−1) aredecoded.

[0033] As described above, the MPEG decoder needs to decode GOP (n−1),which will not be displayed, in addition to GOP (n). Thus, in order toobtain editing results obtained earlier by referring to FIG. 1, GOP (n)is decoded after GOP (m) separated away from GOP (n) is decoded but, inorder to decode GOP (n), it is necessary to decode GOP (n−1) immediatelypreceding GOP (n). Accordingly, by using only a unit of MPEG decoderhaving a 1-time decoding-process speed, there is no time margin todecode GOP (n−1) after decoding GOP (m) but before decoding GOP (n).

[0034] As a result, by using only a unit of MPEG decoder having a 1-timedecoding-process speed, on the basis of an edit-point list, it isimpossible to reproduce results of editing an MPEG screen.

[0035] Japanese Patent Laid-open No. 2002-101379 discloses a method toreproduce results of editing an MPEG screen by using two MPEG decoderson the basis of an edit-point list.

[0036] In accordance with the method disclosed in Japanese PatentLaid-open No. 2002-101379, a duration required between a start editpoint and an end edit point must be at least the length of a GOP. Byusing two MPEG decoders to alternately decode an MPEG stream, which hasbeen edited under such a condition, it is possible to reproduce resultsof editing the MPEG screen. The start and end edit points can each be anIN or OUT point. If the start edit point is an IN point, the end editpoint is an OUT point. If the start edit point is an OUT point, on theother hand, the end edit point is an IN point. In the followingdescription, the minimum duration is appropriately referred to as ashortest cut duration or a margin.

[0037] An MPEG stream 211 shown in FIG. 3 is the same as the MPEG stream201 shown in FIG. 1. Assume that a start sequence of GOPs beginning withGOPi not shown in the figure and ending with GOP (m) on an MPEG stream211 is to be reproduced. Then, GOP (n) located after GOP (m) is to bereproduced. Finally, another sequence of GOPs beginning with GOP (m+2)located before GOP (n) and ending with GOPj not shown in the figure isto be reproduced. In order to reproduce these GOPs, a cut editingprocess is carried out to set edit points T₁, T₂, T₃ and T₄.

[0038] In this case, in an operation to reproduce these results of theediting, the start sequence of GOPs ending with picture P15 at the tailof GOP (m) is first displayed to be followed by pictures B1 to P15 ofGOP (n) before displaying the other sequence of GOPs beginning withpicture B1 at the head of GOP (m+2) as is obvious from apicture-displaying order 212 shown in FIG. 3. At the tail of GOP (m),the edit point T₁, has been set as an OUT point. At pictures B1 and P15of GOP (n), the edit points T₃ and T₄ have been set as IN and OUT pointsrespectively. At the head of GOP (m+2), the edit point T₂ has been setas an IN point.

[0039] In order to obtain a picture-displaying order 212 shown in FIG.3, in accordance with the method disclosed in Japanese Patent Laid-openNo. 2002-101379, a specific one of 2 MPEG decoders #1 and #2, is used todecode all pictures ending with GOP (m) as shown in a picture-decodingorder 213 of FIG. 3. For example, the specific MPEG decoder is MPEGdecoder #1. It is to be noted that, in the process to decode GOP (m),the processing to decode picture B14 to be decoded last among thepictures composing GOP (m) must be completed by a time t₂, at whichpicture B14 is to be displayed. Thus, the process to decode GOP (m) mustbe started before a time leading ahead of the time t₂ by a period oftime it takes to display pictures composing a GOP. In thepicture-decoding order 213 shown in FIG. 3, a time t₁, is determined tobe the time to start the process to decode GOP (m).

[0040] The edit point T₁ is reached after decoder #1 has decoded GOP (m)to be displayed. The process then is continued to processing to decodeand display GOP (n). The processing to decode and display GOP (n) muststart at the edit point T₃ and end at the edit point T₄.

[0041] In order to decode GOP (n), it is necessary to decode GOP (n−1)immediately preceding GOP (n) as described earlier. In the process todecode GOP (n), the processing to decode picture B14 to be decoded lastamong the pictures composing GOP (n) must be completed by a time t₃, atwhich picture B14 is to be displayed. Thus, the process to decode GOP(n) must be started before a time leading ahead of the time t₃ by aperiod of time it takes to display pictures composing a GOP. In apicture-decoding order 214 shown in FIG. 3, a time t₂ is determined tobe the time to start the process to decode GOP (n). By the same token,the process to decode GOP (n−1) immediately preceding GOP (n) must bestarted before a time leading ahead of the time t₂ by a period of timeit takes to display pictures composing a GOP in the picture-decodingorder 214 shown in FIG. 3, a time t₁ is determined to be the time tostart the process to decode GOP (n−1).

[0042] For the reason described above, MPEG decoder #2 starts decodingGOP (n−1) at the time t₁ and continues the process by decoding GOP (n)as shown in the picture-decoding order 214 of FIG. 3. MPEG decoder #2 isthe other one of two decoders #1 and #2.

[0043] In the mean time, MPEG decoder #1 should naturally terminate thedecoding process at the end of the processing to decode GOP (m). AfterGOP (n) is decoded by decoder #2 and displayed, however, the edit pointT₄ is reached. Then, MPEG decoder #1 must decode the other sequence ofGOPs beginning with GOP (m+2) at the edit point T₂ for a display.

[0044] In order to decode GOP (m+2), it is necessary to decode GOP (m+1)leading ahead of GOP (m+2) by a GOP as described earlier. In the processto decode GOP (m+2), the processing to decode picture B14 to be decodedlast among the pictures composing GOP (m+2) must be completed by a timet₄, at which picture B14 is to be displayed, as shown in thepicture-decoding order 213 of FIG. 3. Thus, the process to decode GOP(m+2) must be started before a time leading ahead of the time t₄ by aperiod of time it takes to display pictures composing a GOP. In thepicture-decoding order 213 shown in FIG. 3, the time t₃ is determined tobe the time to start the process to decode GOP (m+2). By the same token,the process to decode GOP (m+1) leading ahead of GOP (m+2) by a GOP mustbe started before a time leading ahead of the time t₃ by a period oftime it takes to display pictures composing a GOP. In thepicture-decoding order 213 shown in FIG. 3, the time t₂ is determined tobe the time to start the process to decode GOP (m+1).

[0045] The time t₂ is a time at which MPEG decoder #1 ends the processto decode GOP (m). Thus, as soon as the process to decode GOP (m) isended, the process to decode GOP (m+1) can be started immediately.

[0046] As described above, if the shortest cut duration is set at aperiod of time it takes to display a GOP, it is possible to reproduceresults of editing an MPEG stream by using two MPEG recorders forcarrying out the so-called alternate decoding process of GOPs between anedit point and the next edit point.

[0047] In accordance with the method disclosed in Japanese PatentLaid-open No. 2002-101379, however, the shortest cut duration, which isa minimum duration required between a start edit point and an end editpoint, must be the period of time it takes to display a GOP, raising aproblem of restricted freedom of editing.

SUMMARY OF THE INVENTION

[0048] It is an object of the present invention to make restrictions onthe shortest cut duration lenient in a process to seamlessly reproduce aresult of editing the stream in order to enhance the freedom of editingin carrying out a process of editing the stream.

[0049] In order to achieve the object described above, in accordancewith an aspect of the present invention, there is provided a decodingcontrol apparatus, which is used for controlling a process to decodeencoded data obtained as a result of a predictive encoding process andis provided with: a picture detector for determining one or fewestpossible pictures, which must be decoded first before decoding a pictureto be displayed after an edit point set in the encoded data but are notto be displayed; a start-point finder for finding a start pointrepresenting a timing to start a process to decode the one or fewestpossible pictures determined by the picture detector even though the oneor fewest possible pictures are not to be displayed; a decodingcontroller for controlling processes, which are carried out by aplurality of decoders for decoding the encoded data in order to decodethe encoded dat_(a), in picture units on the basis of the start point;and a selector for selecting one of pictures, which are obtained asresults of the processes carried out by the decoders, on the basis ofthe edit point and for outputting the selected picture.

[0050] In accordance with another aspect of the present invention, thereis provided a decoding control method, which is used for controlling aprocess to decode encoded data obtained as a result of a predictiveencoding process and is provided with the steps of: determining one orfewest possible pictures, which must be decoded first before decoding apicture to be displayed after an edit point set in the encoded data butare not to be displayed; finding a start point representing a timing tostart a process to decode the one or fewest possible pictures eventhough the one or fewest possible pictures are not to be displayed;controlling processes, which are carried out by a plurality of decodersfor decoding the encoded data in order to decode the encoded dat_(a), inpicture units, on the basis of the start point; and selecting one ofpictures, which are obtained as results of the processes carried out bythe decoders, on the basis of the edit point and outputting the selectedpicture.

[0051] In accordance with a further aspect of the present invention,there is provided a program for driving a computer to carry out adecoding control process to control a process of decoding encoded dataobtained as a result of a predictive encoding process wherein thedecoding control process includes the steps of: determining one orfewest possible pictures, which must be decoded first before decoding apicture to be displayed after an edit point set in the encoded data butare not to be displayed; finding a start point representing a timing tostart a process to decode the one or fewest possible pictures eventhough the one or fewest possible pictures are not to be displayed;controlling processes, which are carried out by a plurality of decodersfor decoding the encoded data in order to decode the encoded dat_(a), inpicture units; and selecting one of pictures, which are obtained asresults of the processes carried out by the decoders, on the basis ofthe edit point and outputting the selected picture.

[0052] In accordance with a still further aspect of the presentinvention, there is provided a information-processing apparatusincluding: a picture detector for determining one or fewest possiblepictures, which are not to be displayed but must be decoded first beforedecoding a picture to be displayed after an edit point described on anedit-point list, that is, a list of the edit point set in encoded dataobtained as a result of a predictive encoding process; a start-pointfinder for finding a start point representing a timing to start aprocess to decode the one or fewest possible pictures determined by thepicture detector even though the one or fewest possible pictures are notto be displayed; and a decoding control list maker for making a decodingcontrol list describing at least the edit point and the start point asdecoding control information for controlling processes carried out by aplurality of decoders for decoding the encoded data in order to decodethe encoded data.

[0053] In accordance with a still further aspect of the presentinvention, there is provided a information-processing method includingthe steps of: determining one or fewest possible pictures, which are notto be displayed but must be decoded first before decoding a picture tobe displayed after an edit point described on an edit-point list, thatis, a list of the edit point set in encoded data obtained as a result ofa predictive encoding process; finding a start point each representing atiming to start a process to decode the one or fewest possible picturesdetermined by the picture detector even though the one or fewestpossible pictures are not to be displayed; and making a decoding controllist describing at least the edit point and the start point as decodingcontrol information for controlling processes carried out by a pluralityof decoders for decoding the encoded data in order to decode the encodeddata.

[0054] In accordance with a still further aspect of the presentinvention, there is provided a program, which is used for driving acomputer to carry out a predetermined process and is provided with thesteps of: determining one or fewest possible pictures, which are not tobe displayed but must be decoded first before decoding a picture to bedisplayed after an edit point described on an edit-point list, that is,a list of the edit point set in encoded data obtained as a result of apredictive encoding process; finding a start point each representing atiming to start a process to decode the one or fewest possible picturesdetermined by the picture detector even though the one or fewestpossible pictures are not to be displayed; and making a decoding controllist describing at least the edit point and the start point as decodingcontrol information for controlling processes carried out by a pluralityof decoders for decoding the encoded data in order to decode the encodeddata.

[0055] In accordance with a still further aspect of the presentinvention, there is provided a decoding control apparatus, which is usedfor controlling a process to decode encoded data obtained as a result ofa predictive encoding process and is provided with: a decodingcontroller for controlling processes carried out by a plurality ofdecoders for decoding the encoded data in order to decode the encodeddata in picture units on the basis of a decoding control list describingat least an edit point set in the encoded data and a start pointrepresenting a timing to start a process to decode fewest possiblepictures, which are not to be displayed but must be decoded first beforedecoding a picture to be displayed after the edit points, as decodingcontrol information for controlling the processes carried out by thedecoders for decoding the encoded data in order to decode the encodeddata; and a selector for selecting one of pictures, which are obtainedas results of the processes carried out by the decoders, on the basis ofthe decoding control list and for outputting the selected picture.

[0056] In accordance with a still further aspect of the presentinvention, there is provided a decoding control method, which is usedfor controlling a process to decode encoded data obtained as a result ofa predictive encoding process and is provided with the steps of:controlling processes carried out by a plurality of decoders fordecoding the encoded data in order to decode the encoded data in pictureunits on the basis of a decoding control list describing at least anedit point set in the encoded data and a start point representing atiming to start a process to decode fewest possible pictures, which arenot to be displayed but must be decoded first before decoding a pictureto be displayed after the edit point as decoding control information forcontrolling the processes carried out by the decoders for decoding theencoded data in order to decode the encoded data; and selecting one ofpictures, which are obtained as results of the processes carried out bythe decoders, on the basis of the decoding control list and outputtingthe selected picture.

[0057] In accordance with a still further aspect of the presentinvention, there is provided a program for driving a computer to carryout a decoding control process of decoding encoded data obtained as aresult of a predictive encoding process wherein the decoding controlprocess includes the steps of: controlling processes carried out by aplurality of decoders for decoding the encoded data in order to decodethe encoded data in picture units on the basis of a decoding controllist describing at least an edit point set in the encoded data and startpoint representing a timing to start a process to decode fewest possiblepictures, which are not to be displayed but must be decoded first beforedecoding a picture to be displayed after the edit point as decodingcontrol information for controlling the processes carried out by thedecoders for decoding the encoded data in order to decode the encodeddata; and selecting one of pictures, which are obtained as results ofthe processes carried out by the decoders, on the basis of the decodingcontrol list and outputting the selected picture.

BRIEF DESCRIPTION OF THE DRAWINGS

[0058]FIG. 1 is an explanatory diagram to be referred to in describing aprocess to reproduce an MPEG stream on the basis of an edit-point list;

[0059]FIG. 2 is an explanatory diagram to be referred to in describing aprocess to decode and then display an MPEG stream;

[0060]FIG. 3 is an explanatory diagram to be referred to in describing astudy case in which it is possible to seamlessly reproduce an MPEGstream;

[0061]FIG. 4 is an explanatory diagram to be referred to in describinganother study case in which it is not possible to seamlessly reproducean MPEG stream;

[0062]FIG. 5 is a block diagram showing a typical configuration of anembodiment implementing a disc system to which the present invention isapplied;

[0063]FIG. 6 shows a flowchart to be referred to in explaining areproduction process carried out by the disc system;

[0064]FIG. 7 is a diagram showing a sequence of pictures to be decodedsequentially by a decoding unit 4;

[0065]FIG. 8 is an explanatory diagram to be referred to in describing afurther study case in which it is possible to seamlessly reproduce anMPEG stream;

[0066]FIG. 9 is an explanatory diagram to be referred to in describing astill further study case in which it is not possible to seamlesslyreproduce an MPEG stream;

[0067]FIG. 10 is an explanatory diagram to be referred to in describingpreparatorily decoded pictures and preparatory decoding times;

[0068]FIG. 11 shows a flowchart to be referred to in explaining aprocess to determine preparatorily decoded pictures;

[0069]FIG. 12 is a block diagram showing a typical configuration ofanother embodiment implementing a disc system to which the presentinvention is applied;

[0070]FIG. 13 is an explanatory diagram to be referred to in describinga reproduction process using a decoding unit 4 comprising decoders 4 ₁to 4 ₃;

[0071]FIG. 14 is an explanatory diagram to be referred to in describinga reproduction process using a decoding unit 4 comprising decoders 4 ₁to 4 ₄;

[0072]FIG. 15 is an explanatory diagram to be referred to in describinga reproduction process using a decoding unit 4 comprising decoders 4 ₁to 4 ₇;

[0073]FIG. 16 is a diagram showing a relation between the number ofdecoders 4 ₁ to 4 _(k) (K) composing the decoding unit 4 and a shortestcut duration;

[0074]FIG. 17 shows a flowchart to be referred to in explaining areproduction process carried out by the disc system;

[0075]FIG. 18 is a diagram showing an edit-point table;

[0076]FIG. 19 shows a flowchart to be referred to in explaining aprocess carried out by the disc system to make a decoding control list;

[0077]FIG. 20 is an explanatory diagram showing an edit-point list and adecoding control list made on the basis of the edit-point list;

[0078]FIG. 21 is a diagram showing a typical edit-point list;

[0079]FIG. 22 is a diagram showing a typical decoding control list;

[0080]FIG. 23 shows a flowchart to be referred to in explaining areproduction process carried out by the disc system;

[0081]FIG. 24 is a diagram showing another typical decoding controllist;

[0082]FIG. 25 shows a flowchart to be referred to in explaining areproduction process carried out by the disc system; and

[0083]FIG. 26 is a diagram showing a typical configuration of anembodiment implementing a computer to which the present invention isapplied.

PREFERRED EMBODIMENTS OF THE INVENTION

[0084] Before explaining preferred embodiments of the present invention,the shortest cut duration is explained. Consider a process to reproduceresults of editing in the same way as that described above. In theresults of editing, an edit point T₄ is not set at picture P15 to bedisplayed last among the pictures composing GOP (n) as shown in apicture-displaying order 221 of FIG. 4, but set at picture B14 to bedisplayed immediately before picture P15 as shown in apicture-displaying order 222 of the same figure. In this process, theduration from an edit point T₃ set at picture B1 at the beginning of GOP(n) to the next edit point, which is the edit point T₄ set at pictureB14 of same GOP (n), is smaller that the duration of a GOP, resulting ina state of an unsatisfied requirement of the shortest cut duration.

[0085] In this case, in an operation to reproduce these results of theediting, the start sequence of GOPs ending with picture P15 at the tailof GOP (m) needs to be first displayed to be followed by pictures B1 toB14 of GOP (n) before displaying the other sequence of GOPs beginningwith picture B1 at the head of GOP (m+2) as is obvious from apicture-displaying order 222 shown in FIG. 4. At the tail of GOP (m),the edit point T₁ has been set. At pictures B1 and B14 of GOP (n), theedit points T₃ and T₄ have been set respectively. At the head of GOP(m+2), the edit point T₂ has been set.

[0086] In the operation to reproduce these results of editing, aspecific one of two MPEG decoders #1 and #2 is used to decode allpictures ending with GOP (m) as shown in a picture-decoding order 223 ofFIG. 4. For example, the specific MPEG decoder is MPEG decoder #1. It isto be noted that, in the process to decode GOP (m), the processing todecode picture B14 to be decoded last among the pictures composing GOP(m) must be completed by a time t₂, at which picture B14 is to bedisplayed, as is the case with the afore described picture-decodingorder 213 of FIG. 3. Thus, the process to decode GOP (m) must be startedbefore a time leading ahead of the time t₂ by a period of time it takesto display pictures composing a GOP. In the picture-decoding order 213shown in FIG. 3, a time t₁ is determined to be the time to start theprocess to decode GOP (m).

[0087] The edit point T₁ is reached after decoder #1 has decoded GOP (m)to be displayed. The process is then continued to processing to decodeand display pictures B1 to B14 of GOP (n). The processing to decode anddisplay GOP (n) must start at the edit point T₃ and end at the editpoint T₄.

[0088] In order to decode GOP (n), it is necessary to first decode GOP(n−1) immediately preceding GOP (n) as described earlier. In the processto decode GOP (n), the processing to decode picture B14 to be decodedlast among the pictures composing GOP (n) must be completed by a timet₃, at which picture B14 is to be displayed. Thus, the process to decodeGOP (n) must be started before a time leading ahead of the time t₃ by aperiod of time it takes to display pictures composing a GOP. In apicture-decoding order 225 shown in FIG. 4, a time t₂ is determined tobe the time to start the process to decode GOP (n). By the same token,the process to decode GOP (n−1) immediately preceding GOP (n) must bestarted before a time leading ahead of the time t₂ by a period of timeit takes to display pictures composing a GOP. In the picture-decodingorder 225 shown in FIG. 4, a time t₁ is determined to be the time tostart the process to decode GOP (n−1).

[0089] For the reason described above, MPEG decoder #2 starts decodingGOP (n−1) at the time t₁ and continues the process by decoding GOP (n)as shown in the picture-decoding order 225 of FIG. 4. MPEG decoder #2 isthe other one of 2 decoders #1 and #2.

[0090] In the mean time, MPEG decoder #1 should naturally terminate thedecoding process at the end of the processing to decode GOP (m). AfterGOP (n) is decoded by decoder #2 and displayed, however, the edit pointT₄ is reached. Then, MPEG decoder #1 must decode the other sequence ofGOPs beginning with GOP (m+2) at the edit point T₂ for a display.

[0091] In order to decode GOP (m+2), it is necessary to first decode GOP(m+1) leading ahead of GOP (m+2) by a GOP as described earlier. In theprocess to decode GOP (m+2), the processing to decode picture B14 to bedecoded last among the pictures composing GOP (m+2) must be completed bya time t₄′, at which picture B14 is to be displayed, as shown in apicture-decoding order 224 of FIG. 4.

[0092] In this case, the edit point T₄ has been set at picture B14immediately preceding picture P15, which is the last picture in thedisplay order of GOP (n), as shown the picture-displaying order 222shown in FIG. 4. Thus, picture P15 pertaining to GOP (n) is notdisplayed. That is to say, after picture B14 pertaining to GOP (n) hasbeen displayed, picture B1 of GOP (m+2), at which the edit point T₂ hasbeen set, is displayed without displaying picture P15 pertaining to GOP(n). Picture B1 pertaining to GOP (m+2) is the first picture in thedisplay order of GOP (m+2). In the case of the case study shown in FIG.4, the display time of GOP (m+2) is thus earlier than that of theconventional method shown in FIG. 3 by a period of time it takes todecode one picture.

[0093] For the reason described above, in the process to decode GOP(m+2) in accordance with the case study shown in FIG. 4, the processingto decode picture B14 to be decoded last among the pictures composingGOP (m+2) must be completed by the time t₄′ leading ahead of the time t₄of the conventional method shown in FIG. 3 by a period of time it takesto decode one picture.

[0094] As is the case with the conventional method shown in FIG. 3, theprocess to decode GOP (m+2) must be started before a time leading aheadof the time t₄′ by a period of time it takes to decode picturescomposing a GOP. In the picture-decoding order 224 shown in FIG. 4, atime t₃′ is determined to be the time to start the process to decode GOP(m+2). By the same token, the process to decode GOP (m+1) leading aheadof GOP (m+2) by a GOP must be started before a time leading ahead of thetime t₃′ by a period of time it takes to decode pictures composing aGOP. In the picture-decoding order 224 shown in FIG. 4, a time t₂′ isdetermined to be the time to start the process to decode GOP (m+1).

[0095] The time t₂′ leads ahead of the time t₂, at which MPEG decoder #1completes the processing to decode GOP (m), by a period of time it takesto decode one picture. At the time t₂, MPEG decoder #1 starts anoperation to decode picture B14 of GOP (m) as shown in thepicture-decoding order 223 of FIG. 4.

[0096] Thus, when the duration between the edit point T₃ and the nextedit point T₄ does not satisfy the requirement of the shortest cutduration as shown in the picture-displaying order 222 of FIG. 4, MPEGdecoder #1 is not capable of starting an operation to decode GOP (m+1)at the time t₂′ so that it is impossible to seamlessly reproduce theresults of editing in accordance with the edit-point list.

[0097] If the shortest cut duration is limited to a GOP, on the otherhand, there is raised a problem of restricted freedom of editing.

[0098] In accordance with the present invention, however, it is possibleto make the limitation imposed on the shortest cut duration more lenientwhile enhancing the freedom of editing.

[0099]FIG. 5 is a diagram showing a typical configuration of anembodiment implementing a disc system provided by the present invention.In this context, the technical term ‘system’ means a set of a pluralityof apparatus logically combined with each other without regard towhether or not the apparatus composing the set is put in the same box.

[0100] An optical disc 1 typically contains a recorded MPEG streamobtained as a result of carrying out an MPEG encoding process on amoving picture. In addition, the optical disc 1 also includes anedit-point list made as another result of editing the recorded MPEGstream as a raw editing material.

[0101] A disc drive 2 has a configuration allowing the optical disc 1 tobe mounted on and demounted from the disc drive 2. The disc drive 2 is acomponent for reading out the MPEG stream as well as the edit-point listfrom the optical disc 1 and outputting the MPEG stream as well as theedit-point list to a bus 3.

[0102] A decoding unit 4 includes a plurality of decoders. For example,the decoding unit 4 has two decoders, namely decoders 4 ₁ and 4 ₂. Thedecoders 4 ₁ and 4 ₂ each issue a request for a portion of the MPEGstream to the disc drive 2 by way of the bus 3. Portions of the MPEGstream, which are output by the disc drive 2 at such a request, aresupplied to the decoders 4 ₁ and 4 ₂ by way of the bus 3. In addition,the decoders 4 ₁ and 4 ₂ each carry out an MPEG decoding process on thereceived portions of the MPEG stream in accordance with control executedby a controller 7, and output pictures obtained as a result of the MPEGdecoding process to a switcher 5.

[0103] It is to be noted that the decoders 4 ₁ and 4 ₂ composing thedecoding unit 4 are assumed to operate at a 1-time decoding processspeed even though the decoders 4 ₁ and 4 ₂ can each be a decoderoperating at a speed other than the one-time decoding process speed. Inaddition, the disc drive 2 reads out an MPEG stream from the opticaldisc 1 at a read-out speed (or a transfer band) large enough for anoperation to supply the MPEG stream to the decoders 4 ₁ and 4 ₂.

[0104] The switcher 5 is a component for selecting either a picturedecoded by the decoders 4 ₁ or a picture decoded by the decoder 4 ₂ inaccordance with control executed by the controller 7, and outputting aselected picture to a display unit 6. The display unit 6 is a componentfor displaying a picture output by the switcher 5. Thus, the displayunit 6 displays whichever picture the switcher 5 selects among a picturedecoded by the decoders 4 ₁ and a picture decoded by the decoders 4 ₂.It is to be noted that the display unit 6 can be an external componentconnected to the disc system shown in FIG. 5.

[0105] The controller 7 is a component for controlling the disc drive 2,the decoding unit 4 and the switcher 5 in accordance with an operationsignal received from an operation unit 8. To put it in detail, whenreceiving an operation signal requesting the disc system to reproduce aresult of an operation to edit an MPEG stream in accordance with anedit-point list from the operation unit 8, the controller 7 issues arequest for the edit-point list to the disc drive 2. The controller 7then receives the edit-point list, which has been read out by the discdrive 2 from the optical disc 1 at the request, from the disc drive 2 byway of the bus 3. Subsequently, the controller 7 detects edit pointsincluded on the edit-point list. In addition, for each of the editpoints detected from the edit-point list, the controller 7 identifiesfewest possible pictures, which are not to be displayed after the editpoint but must be decoded first in order to decode pictures to bedisplayed after the edit point. Then, the controller 7 computes a startpoint representing a timing to start an operation to decode the one orfewest possible pictures not to be displayed after the edit point.Furthermore, the controller 7 controls operations, which are carried outby the decoders 4 ₁ and 4 ₂ to decode the MPEG stream in picture units,on the basis of the start point. Moreover, for each of the edit pointsdetected from the edit-point list, the controller 7 controls theswitcher 5, driving the switcher 5 to select either a picture decoded bythe decoder 4 ₁ or a picture decoded by the decoder 4 ₂ and output theselected picture.

[0106] The operation unit 8 is a component operated by the user tooutput an operation signal representing an operation carried out by theuser on the operation unit 8 to the controller 7.

[0107] The disc system with the configuration described above carriesout a reproduction process to reproduce an MPEG stream from the opticaldisc 1 in accordance with an edit-point list, which has also beenrecorded on the same optical disc 1.

[0108]FIG. 6 shows a flowchart representing the reproduction processcarried out by the disc system shown in FIG. 5.

[0109] When the user operates the operation unit 8 to start a process toreproduce a result of an operation to edit an MPEG stream in accordancewith an edit-point list, the operation unit 8 outputs an operationsignal to start the reproduction process to the controller 7. Theoperation signal to start the reproduction process is properly referredto hereafter as a reproduction start operation signal.

[0110] Receiving the reproduction start operation signal from theoperation unit 8 at a step S1, the controller 7 issues a request for theedit-point list to the disc drive 2. At this request, the disc drive 2reads out the edit-point list from the optical disc 1 and then outputsthe list to the bus 3. The controller 7 then receives the edit-pointlist from the bus 3. Then, at the next step S2, the controller 7 setsschedules of sequences of pictures to be decoded by the decoders 4 ₁ and4 ₂ and a schedule of a select pattern for driving the switcher 5 toselect the output of either the decoders 4 ₁ or the decoder 4 ₂.

[0111] Subsequently, at the next step S3, the controller 7 controls thedecoders 4 ₁ and 4 ₂ as well as the switcher 5 in accordance with theschedules set at the step S2.

[0112] In accordance with the control executed by the controller 7, thedecoders 4 ₁ and 4 ₂ issue a request for portions of an MPEG stream tothe disc drive 2 by way of the bus 3. Then, the decoders 4 ₁ and 4 ₂decode the requested portions of the MPEG stream, which are supplied bythe disc drive 2 by way of the bus 3. The decoders 4 ₁ and 4 ₂ thenoutput pictures obtained as a result of decoding to the switcher 5.Subsequently, the switcher 5 selects a decoded picture output by eitherthe decoder 1 or the decoder 2 and outputs the selected picture to thedisplay unit 6.

[0113] Then, at the next step S4, the controller 7 forms a judgment asto whether or not the user has operated the operation unit 8 to stop thereproduction process. If the outcome of the judgment formed at the stepS4 indicates that the user has operated the operation unit 8 to stop thereproduction process, that is, if the controller 7 has received anoperation signal to stop the reproduction process from the operationunit 8, the reproduction process is ended. The operation signal to stopthe reproduction process is properly referred to hereafter as areproduction stop operation signal.

[0114] If the outcome of the judgment formed at the step S4 indicatesthat the user has not operated the operation unit 8 to stop thereproduction process, on the other hand, the flow of the reproductionprocess goes on to a step S5 at which the controller 7 forms a judgmentas to whether or not the process to reproduce the result of an operationto edit the MPEG stream in accordance with an edit-point list read outat the step S1 has been completed. If the outcome of the judgment formedat the step S5 indicates that the process to reproduce the result of anoperation to edit the MPEG stream in accordance with an edit-point listhas not been completed, the flow of the reproduction process goes backto the step S3 to repeat the same processing. If the outcome of thejudgment formed at the step S5 indicates that the process to reproducethe result of an operation to edit the MPEG stream in accordance with anedit-point list has been completed, on the other hand, the execution ofthe reproduction process is ended.

[0115] The following description explains the processing carried out bythe controller 7 at the step S2 of the flowchart shown in FIG. 6 to setschedules of sequences of pictures to be decoded by the decoders 4 ₁ and4 ₂. It is to be noted that, in this embodiment, a GOP typicallyincludes pictures arranged in a sequence of B1, B2, I3, B4, B5, P6, B7,B8, P9, B10, B11, P12, B13, B14, P15 and encoded/decoded in an order ofI3, B1, B2, P6, B4, B5, P9, B7, B8, P12, B10, B11, P15, B13, B14. It isalso worth noting, however, that the configuration of a GOP is notlimited to the above sequence.

[0116] The controller 7 specifies pictures to be decoded by the decoders4 ₁ or 4 ₂ in processing to decode the MPEG stream, and requests thedecoders 4 ₁ and 4 ₂ to decode only fewest possible pictures, which arenot to be displayed after an edit point but must be first decoded inorder to decode pictures to be displayed after the edit point. In thisway, the requirement of the shortest cut duration can be made morelenient.

[0117] That is to say, it may be necessary to decode GOP (n−1)immediately preceding GOP (n) in order to decode GOP (n) itself asdescribed before.

[0118] To put it concretely, in order to decode pictures B1 and B2pertaining to GOP (n), it is necessary to reference picture P15pertaining to GOP (n−1) immediately preceding GOP (n). Furthermore, inorder to decode picture P12 pertaining to GOP (n−1), it is necessary toreference picture P9 pertaining to GOP (n−1). In the same way, for otherpictures pertaining to GOP (n−1), in order to decode picture P9, it isnecessary to reference picture P6 and, in order to decode picture P6, itis necessary to reference picture I3.

[0119] In accordance with the conventional technology, the processing todecode pictures is controlled in GOP units. Thus, in order to decodepictures B1 and B2 pertaining to GOP (n), it is necessary to firstdecode all pictures pertaining to GOP (n−1) immediately preceding GOP(n).

[0120] Accordingly, if an edit point is set at picture B1 or B2pertaining to GOP (n), in order to start a display operation beginningwith picture B1 or B2, it is necessary to first decode all picturespertaining to GOP (n−1) even though these pictures are not to bedisplayed before pictures B1 and B2 in the case studies explainedbefore.

[0121] In addition, for pictures pertaining to GOP (n), in order todecode a picture other than pictures B1 and B2, it is necessary toreference a picture pertaining to the same GOP (n) even though it is notnecessary to reference picture pertaining to GOP (n−1) immediatelypreceding GOP (n). In order to decode picture B4 pertaining to GOP (n),for example, it is necessary to first reference pictures I3 and P6,which also pertain to GOP (n). Thus, in order to decode picture B4pertaining to GOP (n), it is necessary to first decode all pictures I3,B1, B2 and P6, which precede picture B4 in the decoding order of GOP(n). Otherwise, picture B4 cannot be decoded.

[0122] Thus, if an edit point is set at picture B4 pertaining to GOP(n), it is necessary to first decode all pictures I3, B1, B2 and P6,which also pertain to GOP (n) and not to be displayed, in order to starta display operation beginning with picture B4.

[0123] In order to implement the above scheme, the controller 7 controlsthe decoders 4 ₁ and 4 ₂ by specifying objects of decoding in pictureunits in place of GOP units. In this way, only pictures that have beendisplayed are referenced in case such pictures are required for decodinganother picture to be displayed. On the other hand, pictures that havenot been displayed are, if possible, not referenced in decoding aspecific picture to be displayed with the exception of as fewest suchpictures as possible.

[0124] That is to say, if objects of decoding are specified in GOPunits, with an edit point set at picture B1 or B2 pertaining to GOP (n),in order to start a display operation beginning with picture B1 or B2,as described above, it is necessary to first decode all picturespertaining to GOP (n−1) even though these pictures are not to bedisplayed before pictures B1 and B2 in the case studies explainedbefore. However, only picture P15 pertaining to GOP (n−1) is actuallyreferenced in decoding pictures B1 and B2 pertaining to GOP (n) and onlypicture P12 pertaining to GOP (n−1) is actually referenced in decodingpicture P15 pertaining to GOP (n−1). By the same token, for otherpictures pertaining to GOP (n−1), only picture P9 is actually referencedin decoding picture P12, only picture P6 is actually referenced indecoding picture P9, and only picture I3 is actually referenced indecoding picture P6.

[0125] Thus, the fewest possible specific pictures of GOP (n−1), whichneed to be decoded first before decoding pictures B1 and B2 pertainingto GOP (n) even though these specific pictures are not to be displayedbefore pictures B1 and B2 in the case studies explained before, are only5 pictures, namely, I3, P6, P9, P12 and P15. Pictures of GOP (n−1),which do not need to be referenced in decoding pictures B1 and B2pertaining to GOP (n), are B1, B2, B4, B5, B7, B8, B10, B11, B13 andB14. It is thus unnecessary to decode the pictures of GOP (n−1), whichare not referenced. A picture not to be displayed is not supplied to thedisplay unit 6 shown in FIG. 5.

[0126] By the same token, if an edit point has been set at picture B4pertaining to GOP (n), for example, fewest possible specific pictures ofGOP (n), which need to be decoded first before decoding picture B4 eventhough these specific pictures are not to be displayed due to thelocation of the edit point, are reduced to only picture I3 pertaining toGOP (n). Since pictures B1 and B2 pertaining to GOP (n) are notreferenced in decoding picture B4 pertaining to GOP (n), it is notnecessary to decode pictures B1 and B2.

[0127] As described earlier, in accordance with the MPEG technique,while an I or P picture can be used as a picture to be referenced indecoding another picture, a B picture is never used as a picture to bereferenced in decoding another picture. Thus, only pictures I and P canbe categorized as fewest possible specific pictures, which need to bedecoded first before decoding other pictures even though these specificpictures are not to be displayed.

[0128] As described earlier, at the step S2 of the flowchart shown inFIG. 6, the controller 7 sets schedules of sequences of pictures, whichare to be decoded by the decoders 4 ₁ and 4 ₂, in accordance with theedit-point list. Typically, the schedule is set as shown in FIG. 7.

[0129] To put it in detail, the controller 7 detects first edit pointsfrom the edit-point list. For each detected edit point set as an INpoint, the controller 7 then sets a schedule of a sequence of picturesto be decoded by the decoders 4 ₁ or 4 ₂ in accordance with a picture atwhich the detected edit point is set.

[0130] To put it concretely, If a detected edit point has been set as anIN point at picture B1 pertaining to GOP (n) as indicated by the firstline of the schedules shown in FIG. 7, for example, the fewest possiblespecific pictures of GOP (n−1), which need to be decoded first beforedecoding picture B1 pertaining to GOP (n) even though these specificpictures are not to be displayed before picture B1 in the case studiesexplained before, are only 5 pictures, namely, I3, P6, P9, P12 and P15as described earlier. Thus, the controller 7 sets a schedule to firstdecode these pictures I3, P6, P9, P12 and P15 pertaining to GOP (n−1).Then, thereafter, subsequent pictures pertaining to GOP (n) need to besequentially decoded. That is to say, the schedule includes decoding ofsubsequent pictures of GOP (n) in the normal decoding order of (I3, B1,B2, P6, B4 and so on) after decoding pictures I3, P6, P9, P12 and P15pertaining to GOP (n−1).

[0131] If a detected edit point has been set as an IN point at pictureB2 pertaining to GOP (n) as indicated by the second line of theschedules shown in FIG. 7, the fewest possible specific pictures of GOP(n−1), which need to be decoded first before decoding picture B2pertaining to GOP (n) even though these specific pictures are not to bedisplayed before picture B2 in the case studies explained before, areonly 5 pictures, namely, I3, P6, P9, P12 and P15 as described earlier.Thus, the controller 7 sets a schedule to first decode these picturesI3, P6, P9, P12 and P15 pertaining to GOP (n−1). Then, thereafter,pictures I3, B1, B2, P6, B4 and so on pertaining to GOP (n) wouldnaturally need to be sequentially decoded. However, picture B1 supposedto be displayed before picture B2, at which a detected edit point hasbeen set as an IN point, need to be neither referenced because pictureB1 is a B picture, nor displayed because the detected edit point hasbeen set at picture B2 following picture B1 in the display order. Thus,it is not necessary to decode picture B1. That is to say, the scheduleincludes decoding of subsequent pictures of GOP (n) in a decoding orderof (I3, B2, P6, B4 and so on) after decoding pictures I3, P6, P9, P12and P15 pertaining to GOP (n−1). That is to say, picture B2 pertainingto GOP (n) is decoded after picture I3 to be followed by decoding ofpictures P6, B4 and so on.

[0132] If a detected edit point has been set as an IN point at pictureI3 pertaining to GOP (n) as indicated by the third line of the schedulesshown in FIG. 7, no other pictures need to be referenced in order todecode picture I3. Thus, pictures I3, B1, B2, P6, B4 and so onpertaining to GOP (n) would naturally need to be sequentially decoded.Since a detected edit point is set as an IN point at picture I3,however, it is not necessary to display pictures B1 and B2, which aresupposed to be displayed before picture I3 following pictures B1 and B2in the display order, and it is also unnecessary to reference picturesB1 and B2 because pictures B1 and B2 are each a B picture. Thus, it isnot necessary to decode pictures B1 and B2. For this reason, thecontroller 7 sets a schedule to decode picture P6 after picture I3without decoding pictures B1 and B2. After decoding picture P6, thepictures remaining in the original decoding sequence are decodedsequentially in the normal order.

[0133] If a detected edit point has been set as an IN point at pictureB4 pertaining to GOP (n) as indicated by the fourth line of theschedules shown in FIG. 7, the fewest possible specific pictures, whichneed to be decoded first before decoding picture B4 even though thesespecific pictures are not to be displayed before picture B4 because ofthe position of the detected edit point, are reduced to only picture I3pertaining to GOP (n). Thus, the controller 7 sets a schedule to firstdecode picture I3 pertaining to GOP (n). Then, thereafter, pictures B1,B2, P6, B4, B5 and so on of GOP (n), which follow picture I3 inaccordance with the normal decoding order, would naturally need to besequentially decoded. However, pictures B1 and B2 supposed to bedisplayed before picture B4, at which a detected edit point has been setas an IN point, need to be neither referenced because pictures B1 and B2are each a B picture, nor displayed because the detected edit point hasbeen set at picture B4 following pictures B1 and B2 in the displayorder. Thus, it is not necessary to decode pictures B1 and B2. For thisreason, the controller 7 sets a schedule to decode picture P6 pertainingto GOP (n) after picture I3 without decoding pictures B1 and B2. Afterdecoding picture P6, the pictures remaining in the original decodingsequence are decoded sequentially in the normal order.

[0134] If a detected edit point has been set as an IN point at pictureB5 pertaining to GOP (n) as indicated by the fifth line of the schedulesshown in FIG. 7, the fewest possible specific pictures, which need to bedecoded first before decoding picture B5 even though these specificpictures are not to be displayed before picture B5 because of theposition of the detected edit point, are reduced to only picture I3pertaining to GOP (n). Thus, the controller 7 sets a schedule to firstdecode picture I3 pertaining to GOP (n). Then, thereafter, pictures B1,B2, P6, B4, B5 and so on of GOP (n), which follow picture I3 inaccordance with the normal decoding order, would naturally need to besequentially decoded. However, pictures B1, B2 and B4 supposed to bedisplayed before picture B5, at which a detected edit point has been setas an IN point, need to be neither referenced because pictures B1, B2and B4 are each a B picture, nor displayed because the detected editpoint has been set at picture B5 following pictures B1, B2 and B4 in thedisplay order. Thus, it is not necessary to decode pictures B1, B2 andB4. For this reason, the controller 7 sets a schedule to decode pictureP6 pertaining to GOP (n) after picture I3 without decoding pictures B1and B2. Then, after decoding picture P6, picture B5 is decoded withoutdecoding picture B4. Thereafter, the pictures remaining in the originaldecoding sequence are decoded sequentially in the normal order.

[0135] If a detected edit point has been set as an IN point at pictureP6 pertaining to GOP (n) as indicated by the sixth line of the schedulesshown in FIG. 7, the fewest possible specific pictures, which need to bedecoded first before decoding picture P6 even though these specificpictures are not to be displayed before picture P6 because of theposition of the detected edit point, are reduced to only picture I3pertaining to GOP (n). Thus, the controller 7 sets a schedule to firstdecode picture I3 pertaining to GOP (n). Then, thereafter, pictures B1,B2, P6, B4, B5, P9 and so on of GOP (n), which follow picture I3 inaccordance with the normal decoding order, would naturally need to besequentially decoded. However, pictures B1, B2, B4 and B5 supposed to bedisplayed before picture P6, at which a detected edit point has been setas an IN point, need to be neither referenced because pictures B1, B2,B4 and B5 are each a B picture, nor displayed because the detected editpoint has been set at picture P6 following pictures B1, B2, B4 and B5 inthe display order. Thus, it is not necessary to decode pictures B1, B2,B4 and B5. For this reason, the controller 7 sets a schedule to decodepicture P6 pertaining to GOP (n) after picture I3 without decodingpictures B1 and B2. Then, after decoding picture P6, picture P9 isdecoded without decoding pictures B4 and B5. Thereafter, the picturesremaining in the original decoding sequence are decoded sequentially inthe normal order.

[0136] If a detected edit point has been set as an IN point at pictureB7 pertaining to GOP (n) as indicated by the seventh line of theschedules shown in FIG. 7, the fewest possible specific pictures, whichneed to be decoded first before decoding picture B7 even though thesespecific pictures are not to be displayed before picture B7 because ofthe position of the detected edit point, are reduced to only pictures I3and P6 pertaining to GOP (n). Thus, the controller 7 sets a schedule tofirst decode pictures I3 and P6 pertaining to GOP (n). Then, thereafter,pictures B4, B5, P9, B7, B8 and so on of GOP (n), which follow pictureP6 in accordance with the normal decoding order, would naturally need tobe sequentially decoded. However, pictures B4 and B5 supposed to bedisplayed before picture B7, at which a detected edit point has been setas an IN point, need to be neither referenced because pictures B4 and B5are each a B picture, nor displayed because the detected edit point hasbeen set at picture B7 following pictures B4 and B5 in the displayorder. Thus, it is not necessary to decode pictures B4 and B5. For thisreason, the controller 7 sets a schedule to decode picture P9 pertainingto GOP (n) after picture P6 without decoding pictures B4 and B5.Thereafter, the pictures remaining in the original decoding sequence aredecoded sequentially in the normal order.

[0137] If a detected edit point has been set as an IN point at pictureB8 pertaining to GOP (n) as indicated by the eighth line of theschedules shown in FIG. 7, the fewest possible specific pictures, whichneed to be decoded first before decoding picture B8 even though thesespecific pictures are not to be displayed before picture B8 because ofthe position of the detected edit point, are reduced to only pictures I3and P6 pertaining to GOP (n). Thus, the controller 7 sets a schedule tofirst decode pictures I3 and P6 pertaining to GOP (n). Then, thereafter,pictures B4, B5, P9, B7, B8 and so on of GOP (n), which follow pictureP6 in accordance with the normal decoding order, would naturally need tobe sequentially decoded. However, pictures B4, B5 and B7 supposed to bedisplayed before picture B8, at which a detected edit point has been setas an IN point, need to be neither referenced because pictures B4, B5and B7 are each a B picture, nor displayed because the detected editpoint has been set at picture B8 following pictures B4, B5 and B7 in thedisplay order. Thus, it is not necessary to decode pictures B4, B5 andB7. For this reason, the controller 7 sets a schedule to decode pictureP9 pertaining to GOP (n) after picture P6 without decoding pictures B4and B5. Then, after decoding picture P9, picture B8 is decoded withoutdecoding picture B7. Thereafter, the pictures remaining in the originaldecoding sequence are decoded sequentially in the normal order.

[0138] If a detected edit point has been set as an IN point at pictureP9 pertaining to GOP (n) as indicated by the ninth line of the schedulesshown in FIG. 7, the fewest possible specific pictures, which need to bedecoded first before decoding picture P9 even though these specificpictures are not to be displayed before picture P9 because of theposition of the detected edit point, are reduced to only pictures I3 andP6 pertaining to GOP (n). Thus, the controller 7 sets a schedule tofirst decode pictures I3 and P6 pertaining to GOP (n). Then, thereafter,pictures B4, B5, P9, B7, B8, P12, B10, B11 and so on of GOP (n), whichfollow picture P6 in accordance with the normal decoding order, wouldnaturally need to be sequentially decoded. However, pictures B4, B5, B7and B8 supposed to be displayed before picture P9, at which a detectededit point has been set as an IN point, need to be neither referencedbecause pictures B4, B5, B7 and B8 are each a B picture, nor displayedbecause the detected edit point has been set at picture P9 followingpictures B4, B5, B7 and B8 in the display order. Thus, it is notnecessary to decode pictures B4, B5, B7 and B8. For this reason, thecontroller 7 sets a schedule to decode picture P9 pertaining to GOP (n)after picture P6 without decoding pictures B4 and B5. Then, afterdecoding picture P9, picture P12 is decoded without decoding pictures B7and B8. Thereafter, the pictures remaining in the original decodingsequence are decoded sequentially in the normal order.

[0139] If a detected edit point has been set as an IN point at pictureB10 pertaining to GOP (n) as indicated by the tenth line of theschedules shown in FIG. 7, the fewest possible specific pictures, whichneed to be decoded first before decoding picture B10 even though thesespecific pictures are not to be displayed before picture B10 because ofthe position of the detected edit point, are reduced to only picturesI3, P6 and P9 pertaining to GOP (n). Thus, the controller 7 sets aschedule to first decode pictures I3, P6 and P9 pertaining to GOP (n).Then, thereafter, pictures B7, B8, P12, B10, Bl1 and so on of GOP (n),which follow picture P9 in accordance with the normal decoding order,would naturally need to be sequentially decoded. However, pictures B7and B8 supposed to be displayed before picture B10, at which a detectededit point has been set as an IN point, need to be neither referencedbecause pictures B7 and B8 are each a B picture, nor displayed becausethe detected edit point has been set at picture B10 following picturesB7 and B8 in the display order. Thus, it is not necessary to decodepictures B7 and B8. For this reason, the controller 7 sets a schedule todecode picture P12 pertaining to GOP (n) after picture P9 withoutdecoding pictures B7 and B8. Thereafter, the pictures remaining in theoriginal decoding sequence are decoded sequentially in the normal order.

[0140] If a detected edit point has been set as an IN point at pictureB11 pertaining to GOP (n) as indicated by the eleventh line of theschedules shown in FIG. 7, the fewest possible specific pictures, whichneed to be decoded first before decoding picture B11 even though thesespecific pictures are not to be displayed before picture B11 because ofthe position of the detected edit point, are reduced to only picturesI3, P6 and P9 pertaining to GOP (n). Thus, the controller 7 sets aschedule to first decode pictures I3, P6 and P9 pertaining to GOP (n).Then, thereafter, pictures B7, B8, P12, B10, B11 and so on of GOP (n),which follow picture P9 in accordance with the normal decoding order,would naturally need to be sequentially decoded. However, pictures B7,B8 and B10 supposed to be displayed before picture B11, at which adetected edit point has been set as an IN point, need to be neitherreferenced because pictures B7, B8 and B10 are each a B picture, nordisplayed because the detected edit point has been set at picture B11following pictures B7, B8 and B10 in the display order. Thus, it is notnecessary to decode pictures B7, B8 and B10. For this reason, thecontroller 7 sets a schedule to decode picture P12 pertaining to GOP (n)after picture P9 without decoding pictures B7 and B8. Then, afterdecoding picture P12, picture B11 is decoded without decoding pictureB10. Thereafter, the pictures remaining in the original decodingsequence are decoded sequentially in the normal order.

[0141] If a detected edit point has been set as an IN point at pictureP12 pertaining to GOP (n) as indicated by the twelfth line of theschedules shown in FIG. 7, the fewest possible specific pictures, whichneed to be decoded first before decoding picture P12 even though thesespecific pictures are not to be displayed before picture P12 because ofthe position of the detected edit point, are reduced to only picturesI3, P6 and P9 pertaining to GOP (n). Thus, the controller 7 sets aschedule to first decode pictures I3, P6 and P9 pertaining to GOP (n).Then, thereafter, pictures B7, B8, P12, B10, B11, P15, B13, B14 and soon of GOP (n), which follow picture P9 in accordance with the normaldecoding order, would naturally need to be sequentially decoded.However, pictures B7, B8, B10 and B11 supposed to be displayed beforepicture P12, at which a detected edit point has been set as an IN point,need to be neither referenced because pictures B7, B8, B10 and B11 areeach a B picture, nor displayed because the detected edit point has beenset at picture B12 following pictures B7, B8, B10 and B1 in the displayorder. Thus, it is not necessary to decode pictures B7, B8, B10 and Bl1.For this reason, the controller 7 sets a schedule to decode picture P12pertaining to GOP (n) after picture P9 without decoding pictures B7 andB8. Then, after decoding picture P12, picture P15 is decoded withoutdecoding pictures B10 and B1. Thereafter, the pictures remaining in theoriginal decoding sequence are decoded sequentially in the normal order.

[0142] If a detected edit point has been set as an IN point at pictureB13 pertaining to GOP (n) as indicated by the thirteenth line of theschedules shown in FIG. 7, the fewest possible specific pictures, whichneed to be decoded first before decoding picture B13 even though thesespecific pictures are not to be displayed before picture B13 because ofthe position of the detected edit point, are reduced to only picturesI3, P6, P9 and P12 pertaining to GOP (n). Thus, the controller 7 sets aschedule to first decode pictures I3, P6, P9 and P12 pertaining to GOP(n). Then, thereafter, pictures B10, B11, P15, B13, B14 and so on of GOP(n), which follow picture P12 in accordance with the normal decodingorder, would naturally need to be sequentially decoded. However,pictures B10 and B11 supposed to be displayed before picture B13, atwhich a detected edit point has been set as an IN point, need to beneither referenced because pictures B10 and B11 are each a B picture,nor displayed because the detected edit point has been set at pictureB13 following pictures B10 and B11 in the display order. Thus, it is notnecessary to decode pictures B10 and B11. For this reason, thecontroller 7 sets a schedule to decode picture P15 pertaining to GOP (n)after picture P12 without decoding pictures B10 and Bl1. Thereafter, thepictures remaining in the original decoding sequence are decodedsequentially in the normal order.

[0143] If a detected edit point has been set as an IN point at pictureB14 pertaining to GOP (n) as indicated by the fourteenth line of theschedules shown in FIG. 7, the fewest possible specific pictures, whichneed to be decoded first before decoding picture B14 even though thesespecific pictures are not to be displayed before picture B14 because ofthe position of the detected edit point, are reduced to only picturesI3, P6, P9 and P12 pertaining to GOP (n). Thus, the controller 7 sets aschedule to first decode pictures I3, P6, P9 and P12 pertaining to GOP(n). Then, thereafter, pictures B10, B11, P15, B13, B14 and so on of GOP(n), which follow picture P12 in accordance with the normal decodingorder, would naturally need to be sequentially decoded. However,pictures B10, B11 and B13 supposed to be displayed before picture B14,at which a detected edit point has been set as an IN point, need to beneither referenced because pictures B10, B11 and B13 are each a Bpicture, nor displayed because the detected edit point has been set atpicture B14 following pictures B10, B11 and B13 in the display order.Thus, it is not necessary to decode pictures B10, Bl1 and B13. For thisreason, the controller 7 sets a schedule to decode picture P15pertaining to GOP (n) after picture P12 without decoding pictures B10and B11. Then, after decoding picture P15, picture B14 is decodedwithout decoding pictures B13. Thereafter, the pictures remaining in theoriginal decoding sequence are decoded sequentially in the normal order.

[0144] If a detected edit point has been set as an IN point at pictureP15 pertaining to GOP (n) as indicated by the fifteenth line of theschedules shown in FIG. 7, the fewest possible specific pictures, whichneed to be decoded first before decoding picture P15 even though thesespecific pictures are not to be displayed before picture P15 because ofthe position of the detected edit point, are reduced to only picturesI3, P6, P9 and P12 pertaining to GOP (n). Thus, the controller 7 sets aschedule to first decode pictures I3, P6, P9 and P12 pertaining to GOP(n). Then, thereafter, pictures B10, B11, P15, B13, B14 and so on of GOP(n), which follow picture P12 in accordance with the normal decodingorder, would naturally need to be sequentially decoded. However,pictures B10, B11, B13 and B14 supposed to be displayed before pictureP15, at which a detected edit point has been set as an IN point, need tobe neither referenced because pictures B10, B11, B13 and B14 are each aB picture, nor displayed because the detected edit point has been set atpicture P15 following pictures B10, B11, B13 and B14 in the displayorder. Thus, it is not necessary to decode pictures B10, B11, B13 andB14. For this reason, the controller 7 sets a schedule to decode pictureP15 pertaining to GOP (n) after picture P12 without decoding picturesB10 and B11. Then, after decoding picture P15, picture I3 pertaining tothe next GOP is decoded without decoding pictures B13 and B14.Thereafter, subsequent pictures are decoded sequentially in the normaldecoding order.

[0145] By setting schedules as described above, the disc system shown inFIG. 5 is capable of decoding an MPEG stream at a shortest cut durationof 6 frames (or 6 pictures) as shown in FIG. 8.

[0146] To put it in detail, in the case study shown in FIG. 3, the editpoint T₁ is set at picture P15 pertaining to GOP (m) as an OUT point,the edit point T₃ is set at picture B1 pertaining to GOP (n) as an INpoint, the edit point T₄ is set at picture P15 pertaining to GOP (n) asan OUT point and the edit point T₂ is set at picture B1 pertaining toGOP (m+2) as an IN point as indicated by a picture-displaying order 231shown in FIG. 8. Now, the picture-displaying order 231 is changed to apicture-displaying order 232 also shown in FIG. 8. In accordance withthe picture-displaying order 232, the edit point T1 is set at picture P6pertaining to GOP (m) instead of being set at picture P15 as an OUTpoint and the edit point T₄ is set at picture P6 pertaining to GOP (n)instead of being set at picture P15 as an OUT point.

[0147] As a result of such a change, the duration between the edit pointT₃ set at picture B1 pertaining to GOP (n) as an IN point and the editpoint T₄ set at picture P6 pertaining to GOP (n) as an OUT point is ashortest cut duration, which is six frames in this case.

[0148] In this case, in a process to reproduce a result of editing inaccordance with the picture-displaying order 232 shown in FIG. 8, astart sequence of GOPs is first reproduced to be followed by a middlesequence of GOPs before finally displaying an end sequence of GOPs. Thestart sequence of GOPs ends at the edit point T₁ set at picture P6pertaining to GOP (m) as an OUT point. The middle sequence of GOPsbegins at the edit point T₃ set at picture B1 pertaining to GOP (n) asan IN point and ends at the edit point T₄ set at picture P6 pertainingto GOP (n) as an OUT point. The end sequence of GOPs begins at the editpoint T₂ set at picture B1 pertaining to GOP (m+2) as an IN point.

[0149] In order to carry out the process to reproduce a result ofediting in accordance with the picture-displaying order 232 as describedabove, the controller 7 controls one of the two decoders 4 ₁ and 4 ₂such as the decoders 4 ₁ to decode pictures I3, B1, B2, P6, B4 and B5 tobe displayed as pictures pertaining to GOP (m) as shown in apicture-decoding order 233 of FIG. 8. It is to be noted that, in theprocess to decode pictures I3, B1, B2, P6, B4 and B5 pertaining to GOP(m), the processing to decode picture B5 to be decoded last among thepictures composing GOP (m) must be completed by a time t_(n−2), at whichpicture B5 is to be displayed. Thus, the process to decode GOP (m) mustbe started before a time leading ahead of the time t_(n−2) by a periodof time it takes to display six pictures, namely, pictures B1 to P6. Inthe picture-decoding order 233 shown in FIG. 8, a time t_(n−8) isdetermined to be the time to start the process to decode GOP (m).

[0150] In the case study shown in FIG. 8, reference symbol t_(n) denotesa time at which the display of the first picture B1 pertaining to GOP(n) is started and the display of picture P6 pertaining to GOP (m) isended. Reference symbol t_(n−i) denotes a time leading ahead of the timet_(n) by a period of time it takes to display i frames.

[0151] After the decoders 4 ₁ decodes and displays pictures B1 to P6pertaining to GOP (m), the edit point T₁ is reached as shown in thepicture-displaying order 232 of FIG. 8. The process is then continued toprocessing to decode and display pictures B1 to P6 pertaining to GOP(n). The processing to decode and display GOP (n) must start at the editpoint T₃ and end at the edit point T₄.

[0152] Since picture B1 pertaining to group GOP (n) is a picture atwhich the edit point T₃ has been set, as shown in a picture-decodingorder 235 of FIG. 8, the controller 7 controls the other one of thedecoders 4 ₁ and 4 ₂ (that is, the decoder 4 ₂ in this case) to decodepictures I3, P6, P9, P12 and P15 pertaining to GOP (n−1) immediatelypreceding GOP (n) and then pictures I3, B1, B2, P6, B4 and B5 pertainingto GOP (n) in accordance with the schedule shown on the first lineexplained earlier by referring to FIG. 7. It is to be noted that, in theprocess to decode pictures I3, B1, B2, P6, B4 and B5 pertaining to GOP(n), the processing to decode picture B1 at which the edit point T₃ hasbeen set must be completed by a time t_(n), that is, a point of timepicture B1 is to be displayed. Thus, the process to decode picture I3pertaining to GOP (n−1) must be started before a time leading ahead ofthe time t_(n), by a period of time it takes to display seven picturesbecause the start of the processing to decode picture I3 pertaining toGOP (n−1) leads ahead of the end of the processing to decode picture B1pertaining to GOP (n) by a period of time it takes to display sevenpictures. In the picture-decoding order 235 shown in FIG. 8, a timet_(n−7) is determined to be the time to start the processing to decodeI3 pertaining to GOP (n−1).

[0153] In the mean time, the decoder 4 ₁ ends the decoding process afterthe processing to decode pictures I3, B1, B2, P6, B4 and B5 pertainingto GOP (m) is completed. When the decoders 4 ₁ ends the decodingprocess, the decoding process in the decoder 4 ₂ is going on tillpicture B5 pertaining to GOP (n) is decoded. After picture B5 pertainingto GOP (n) is decoded, the next picture pertaining to GOP (n), namely,picture P6 decoded earlier than picture B5, is displayed. Then, the editpoint T₄ is reached as shown in the picture-displaying order 232 of FIG.8. Thereafter, GOP (m+2) starting at the edit point T₂ and subsequentGOPs must be decoded and displayed.

[0154] Since picture B1 pertaining to group GOP (m+2) is a picture atwhich the edit point T₂ has been set, as shown in a picture-decodingorder 234 of FIG. 8, the controller 7 controls the decoders 4 ₁ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (m+1)immediately preceding GOP (m+2) and then pictures I3, B1, B2, P6, B4, B5and so on pertaining to GOP (m+2) in accordance with the schedule shownon the first line explained earlier by referring to FIG. 7.

[0155] In the process to decode pictures I3, B1, B2, P6, B4, B5 and soon pertaining to GOP (m+2), the processing to decode picture B1 at whichthe edit point T₂ has been set must be completed by a time t_(n)′, thatis, a point of time picture B1 is to be displayed. Thus, the process todecode picture I3 pertaining to GOP (m+1) must be started before a timeleading ahead of the time t_(n)′ by a period of time it takes to displayseven pictures because the start of the processing to decode picture I3pertaining to GOP (m+1) leads ahead of the end of the processing todecode picture B1 pertaining to GOP (m+2) by a period of time it takesto display seven pictures. In the picture-decoding order 234 shown inFIG. 8, a time t_(n−7)′ is determined to be the time to start theprocessing to decode I3 pertaining to GOP (m+1).

[0156] In the case study shown in FIG. 8, reference symbol t_(n)′denotes a time at which the display of the first picture B1 pertainingto GOP (m+2) is started and the display of picture P6 pertaining to GOP(n) is ended. Reference symbol t_(n-i)′ denotes a time leading ahead ofthe time t_(n)′ by a period of time it takes to display i frames.

[0157] In the case study shown in FIG. 8, the time t_(n−2) is a time atwhich the processing carried out by the decoder 4 ₁ to decode picture B5pertaining to GOP (m) is ended. On the other hand, the time t_(n−7)′ isa time at which the processing carried out by the decoders 4 ₁ to decodeGOP (m+1) is started. Thus, the decoding process carried out by thedecoders 4 ₁ does not fail as long as the difference (t_(n−7)′-t_(n−2))is at least 0.

[0158] Let the unity (or 1) represent a period of time it takes todisplay one frame (or one picture). In this case, the times t_(n−2) andt_(n−7)′ can be represented by expressions (t_(n−2)) and (t_(n)′-7)respectively. Thus, the difference (t_(n−7)′−t_(n−2)) can be representedby an expression {(t_(n)′−7)−(t_(n)-2)}=(t_(n)′-t_(n)−5).

[0159] On the other hand, in the case study shown in FIG. 8, the timet_(n) is a time to start an operation to display picture B1 pertainingto GOP (n) as a picture at which the edit point T₃ has been set as an INpoint whereas the time t_(n)′ is a time to end an operation to displaypicture P6 pertaining to GOP (n) as a picture at which the edit point T₄has been set as the OUT point following the IN point. The difference(t_(n)′-t_(n)) is the shortest cut duration, which is 6.

[0160] Accordingly, the difference (t_(n−7)′−t_(n)′-t_(n−2)) is 1 sothat the decoding process carried out by the decoder 4 ₁ does not fail.

[0161] Since the disc system shown in FIG. 5 allows the shortest cutduration to be reduced to as small as a period of time it takes todisplay six frames as described above, the freedom of editing can beimproved.

[0162] If the period between the edit point T₃ set as an IN point andthe edit point T₄ set as the OUT point following the IN point is shorterthan the shortest cut duration, the decoders 4 ₁ will fail.

[0163] Now, consider a reproduction process identical with thereproduction process explained above by referring to FIG. 8 except thatthe picture-displaying order 232 shown in FIG. 8 is changed to apicture-displaying order 24 ₂ shown in FIG. 9. In accordance with thepicture-displaying order 24 ₂, the edit point T₁ is set as an OUT pointat picture B5 pertaining to GOP (m) instead of being set at picture P6immediately following picture B5 and the edit point T₄ is set as an OUTpoint at picture B5 pertaining to GOP (n) instead of being set atpicture P6 immediately following picture B5. As a result of such achange, the duration between the edit point T₃ set at picture B1pertaining to GOP (n) as an IN point and the edit point T₄ set atpicture B5 pertaining to GOP (n) as an OUT point is equal to a period ofonly five frames, which is shorter than the shortest cut duration of sixframes.

[0164] In this case, in a process to reproduce a result of editing inaccordance with the picture-displaying order 24 ₂ shown in FIG. 9, astart sequence of GOPs is first reproduced to be followed by a middlesequence of GOPs before finally displaying an end sequence of GOPs. Thestart sequence of GOPs ends at the edit point T₁ set at picture B5pertaining to GOP (m) as an OUT point. The middle sequence of GOPsbegins at the edit point T₃ set at picture B1 pertaining to GOP (n) asan IN point and ends at the edit point T₄ set at picture B5 pertainingto GOP (n) as an OUT point. The end sequence of GOPs begins at the editpoint T₂ set at picture B1 pertaining to GOP (m+2) as an IN point.

[0165] In order to carry out the process to reproduce a result ofediting in accordance with the picture-displaying order 24 ₂ asdescribed above, the controller 7 controls one of the two decoders 4 ₁and 4 ₂ such as the decoders 4 ₁ to decode pictures I3, B1, B2, P6, B4and B5 to be displayed as pictures pertaining to GOP (m) as shown in apicture-decoding order 243 of FIG. 9. In the case study shown in FIG. 9,picture P6 pertaining to GOP (m) is not displayed. In decoding picturesB4 and B5 pertaining to GOP (m), however, picture P6 is referenced.Thus, picture P6 pertaining to GOP (m) must be decoded first beforepictures B4 and B5.

[0166] It is to be noted that, in the process to decode pictures I3, B1,B2, P6, B4 and B5 pertaining to GOP (m), the processing to decodepicture B5 to be decoded last among the pictures composing GOP (m) mustbe completed by a time t_(n−1), at which picture B5 is to be displayed.Thus, the process to decode GOP (m) must be started before a timeleading ahead of the time t_(n−1) by a period of time it takes todisplay six pictures, namely, pictures B1 to P6. In the picture-decodingorder 243 shown in FIG. 9, a time t_(n−7) is determined to be the timeto start the process to decode GOP (m).

[0167] In the case study shown in FIG. 9, reference symbol t_(n) denotesa time at which the display of the first picture B1 pertaining to GOP(n) is started and the display of picture B5 pertaining to GOP (m) isended.

[0168] After the decoders 4 ₁ decodes pictures B1 to P6 pertaining toGOP (m) and displays only some of the pictures, namely, pictures B1 toB5, the edit point T₁ is reached as shown in the picture-displayingorder 24 ₂ of FIG. 9. The process then is continued to processing todecode pictures B1 to P6 pertaining to GOP (n) and display only some ofthe pictures, namely, pictures B1 to B5. This is because picture P6pertaining to GOP (n) is not displayed. In decoding pictures B4 and B5pertaining to GOP (n), however, picture P6 pertaining to GOP (n) isreferenced. Thus, picture P6 pertaining to GOP (n) must be decoded firstbefore pictures B4 and B5. By the way, the processing to decode anddisplay GOP (n) must start at the edit point T₃ and end at the editpoint T₄.

[0169] Since picture B1 pertaining to group GOP (n) is a picture atwhich the edit point T₃ has been set, as shown in a picture-decodingorder 245 of FIG. 9, the controller 7 controls the other one of the twodecoders 4 ₁ and 4 ₂ (that is, the decoder 4 ₂ in this case) to decodepictures I3, P6, P9, P12 and P15 pertaining to GOP (n−1) immediatelypreceding GOP (n) and then pictures I3, B1, B2, P6, B4 and B5 pertainingto GOP (n) in accordance with the schedule shown on the first lineexplained earlier by referring to FIG. 7. It is to be noted that, in theprocess to decode pictures I3, B1, B2, P6, B4 and B5 pertaining to GOP(n), the processing to decode picture B1 at which the edit point T₃ hasbeen set must be completed by a time t_(n), that is, a point of timepicture B1 is to be displayed. Thus, the process to decode picture I3pertaining to GOP (n−1) must be started before a time leading ahead ofthe time t_(n) by a period of time it takes to display seven picturesbecause the start of the processing to decode picture I3 pertaining toGOP (n−1) leads ahead of the end of the processing to decode picture B1pertaining to GOP (n) by a period of time it takes to display sevenpictures. In the picture-decoding order 245 shown in FIG. 9, a timet_(n−7) is determined to be the time to start the processing to decodeI3 pertaining to GOP (n−1).

[0170] In the mean time, the decoder 4 ₁ ends the decoding process afterthe processing to decode pictures I3, B1, B2, P6, B4 and B5 pertainingto GOP (m) is completed. When the decoders 4 ₁ ends the decodingprocess, the decoding process in the decoder 4 ₂ is going on tillpicture B5 pertaining to GOP (n) is decoded. After picture B5 pertainingto GOP (n) is displayed, the edit point T₄ is reached as shown in thepicture-displaying order 24 ₂ shown in FIG. 9. Thereafter, GOP (m+2)starting at the edit point T₂ and subsequent GOPs must be decoded anddisplayed.

[0171] Since picture B1 pertaining to group GOP (m+2) is a picture atwhich the edit point T₂ has been set, as shown in a picture-decodingorder 24 ₄ of FIG. 9, the controller 7 controls the decoders 4 ₁ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (m+1)immediately preceding GOP (m+2) and then pictures I3, B1, B2, P6, B4, B5and so on pertaining to GOP (m+2) in accordance with the schedule shownon the first line explained earlier by referring to FIG. 7.

[0172] In the process to decode pictures I3, B1, B2, P6, B4, B5 and soon pertaining to GOP (m+2), the processing to decode picture B1 at whichthe edit point T₂ has been set must be completed by a time tn′, that is,a point of time picture B1 is to be displayed. Thus, the process todecode picture I3 pertaining to GOP (m+1) must be started before a timeleading ahead of the time t_(n)′ by a period of time it takes to displayseven pictures because the start of the processing to decode picture I3pertaining to GOP (m+1) leads ahead of the end of the processing todecode picture B1 pertaining to GOP (m+2) by a period of time it takesto display seven pictures. In the picture-decoding order 24 ₄ shown inFIG. 9, a time t_(n−7)′ is determined to be the time to start theprocessing to decode I3 pertaining to GOP (m+1).

[0173] In the case study shown in FIG. 9, reference symbol t_(n)′denotes a time at which the display of the first picture B1 pertainingto GOP (m+2) is started and the display of the last picture B5pertaining to GOP (n) is ended.

[0174] In the picture-decoding orders 243 and 24 ₄ shown in FIG. 9, thetime t_(n−1) is a time at which the processing carried out by thedecoders 4 ₁ to decode picture B5 pertaining to GOP (m) is ended. On theother hand, the time t_(n−7)′ is a time at which the processing carriedout by the decoders 4 ₁ to decode GOP (m+1) is started. Thus, thedecoding process carried out by the decoders 4 ₁ does not fail as longas the difference (t_(n−7)′-t_(n−1)) is at least 0.

[0175] Let the unity (or 1) represent a period of time it takes todisplay one frame (or one picture). In this case, the times t_(n−1) andt_(n−7)′ can be represented by expressions (t_(n)−1) and (t_(n)′7)respectively. Thus, the difference (t_(n−7)′−t_(n)−1) can be representedby an expression {(t_(n)′−7)−(t_(n)−1)}=(t_(n)′−t_(n)−6).

[0176] On the other hand, in the case study shown in FIG. 9, the timet_(n) is a time to start an operation to display picture B1 pertainingto GOP (n) as a picture at which the edit point T₃ has been set as an INpoint whereas the time t_(n)′ is a time to end an operation to displaypicture B5 pertaining to GOP (n) as a picture at which the edit point T₄has been set as the OUT point following the IN point. The difference(t_(n−7)′-t_(n)) is the shortest cut duration, which is only 5 smallerthan 6.

[0177] Accordingly, the difference (t_(n−7)′-t_(n−1)) is −1 so that thedecoding process carried out by the decoder 4 ₁ does fail.

[0178] To put it in detail, in the decoding process carried out by thedecoder 4 ₁, a timing to decode picture B5 pertaining to GOP (m) asshown in the picture-decoding order 243 of FIG. 9 coincides with atiming to decode picture I3 pertaining to GOP (m+1) as shown in thepicture-decoding order 24 ₄ of the same figure. As a result, a seamlessreproduction operation cannot be carried out.

[0179] Next, consider a case in which an edit point is set at a picturepertaining to GOP (m) as an OUT point and another edit point is set at apicture pertaining to GOP (n) as an IN point as shown in FIG. 10. Inthis case, after displaying frame A7, the operation to display frame C4shown in FIG. 10 must be started as shown in a picture-displaying order251 of FIG. 10. Frame A7 pertaining to GOP (m) as shown in FIG. 10 isthe picture at which the aforementioned OUT point is set. On the otherhand, frame C4 pertaining to GOP (n) as shown in FIG. 10 is the pictureat which the aforementioned IN point is set.

[0180] Reference numeral 252 shown in FIG. 10 denotes a sequence ofpictures output by the decoder 4 ₁, which is employed in the disc systemshown in FIG. 5, as a result of decoding. On the other hand, referencenumeral 253 shown in FIG. 10 denotes a sequence of pictures output bythe decoder 4 ₂ as a result of decoding. Thus, the switcher 5 selectsthe pictures output by the decoder 4 ₁, ending with the picture at whichthe OUT point has been set. Thereafter, the switcher 5 selects thepictures output by the decoder 4 ₂, starting with the picture at whichthe IN point has been set.

[0181] The decoder 4 ₂ must thus decode and output the pictures to beselected by the switcher 5, starting with frame C4 at which the IN pointhas been set. In order for the decoder 4 ₂ to decode the pictures to beselected by the switcher 5, fewest possible specific pictures, which arereferenced in decoding the pictures to be selected by the switcher 5even though the specific pictures themselves are not to be displayed,must have been decoded before the processing to decode frame C4 servingas an IN-point picture is decoded as described earlier.

[0182] Let the fewest possible specific pictures, which are referencedin decoding the picture to be selected by the switcher 5 even though thespecific pictures themselves are not to be displayed, be referred to aspreparatorily decoded pictures. Also, let a period of time it takes todecode the preparatorily decoded pictures be referred to as apreparatory decoding time. In the processing to set schedules at thestep S2 of the flowchart shown in FIG. 6, the controller 7 carries outpreparatory-picture computation processing to determine thepreparatorily decoded pictures and find the preparatory decoding time.Then, on the basis of the preparatorily decoded pictures and thepreparatory decoding time, the controller 7 sets schedules of picturesequences to be decoded by the decoders 4 ₁ and 4 ₂.

[0183] The preparatory-picture computation processing carried out by thecontroller 7 is explained by referring to a flowchart shown in FIG. 11as follows.

[0184] In the preparatory-picture computation processing, the controller7 picks one of edit points that are each described on the edit-pointlist as an IN point as an STP. An STP is an IN point that has not beenprocessed before in the preparatory-picture computation processing andmust thus be chosen as an object of processing. At a step S11, thecontroller 7 forms a judgment as to whether or not the specific GOP (n)picture, at which the picked observed edit point STP has been set, ispicture B1 or B2.

[0185] If the outcome of the judgment formed at the step S11 indicatesthat the specific picture, at which the picked observed edit point STPhas been set, is picture B1 or B2, the flow of the processing goes on toa step S12 at which the controller 7 determines pictures I3, P6, P9, P12and P15 pertaining to GOP (n−1) immediately preceding GOP (n) to be thepreparatorily decoded pictures for the observed edit point STP. Then,the flow of the processing goes on to a step S13.

[0186] The controller 7 determines pictures I3, P6, P9, P12 and P15pertaining to GOP (n−1) immediately preceding GOP (n) to be thepreparatorily decoded pictures for the observed edit point STP asfollows.

[0187] The controller 7 searches pictures along the sequence ofdisplayed pictures starting with the picture, at which the observed editpoint STP has been set, in an upstream direction for a first I picture.Then, the controller 7 makes a list of I and P pictures on the sequencein the downstream direction, between the first I picture and thepicture, at which the observed edit point STP has been set. The listincluding the first I picture but excluding the picture, at which theobserved edit point STP has been set, is a list of the preparatorilydecoded pictures.

[0188] At the step S13, the controller 7 computes the picture count ofthe list of the preparatorily decoded pictures, namely, pictures I3, P6,P9, P12 and P15 which have been determined at the step S12. Since thepicture count is five, which is the number of pictures on the list ofpreparatorily decoded pictures I3, P6, P9, P12 ad P15, the controller 7finds out that the preparatory decoding time is equal to a period oftime it takes to decode five frames. Then, the flow of the processinggoes back to the step S11 to repeat the processing described above. Tobe more specific, at this step S11, the controller 7 picks one of editpoints that are each described on the edit-point list as an IN point asa new edit point STP not processed yet in the preparatory-picturecomputation processing.

[0189] If the outcome of the judgment formed at the step S11 indicatesthat the specific picture, at which the picked observed edit point STPhas been set, is neither picture B1 nor B2, on the other hand, the flowof the processing goes on to a step S14. At the step S14, the controller7 forms a judgment as to whether or not the specific GOP (n) picture, atwhich the picked observed edit point STP has been set, is picture I3.

[0190] If the outcome of the judgment formed at the step S14 indicatesthat the specific GOP (n) picture, at which the picked observed editpoint STP has been set, is picture I3, the flow of the processing goeson to a step S15 at which the controller 7 confirms that this specificpicture pertaining to GOP (n) does not have pictures to be preparatorilydecoded for this specific picture. In this case, the flow of theprocessing goes on to a step S16. At the step S16, the controller 7computes the picture count of the list of the preparatorily decodedpictures. In this case, the picture count is zero. Since the picturecount is zero, which is the number of pictures on the list ofpreparatorily decoded pictures, the controller 7 finds out that thepreparatory decoding time is equal to a period of time it takes todecode 0 frames. That is to say, the preparatory decoding time is 0.Then, the flow of the processing goes back to the step S11 to repeat theprocessing described above. To be more specific, at this step S11, thecontroller 7 picks one of edit points that are each described on theedit-point list as an IN point as a new edit point STP not processed yetin the preparatory-picture computation processing.

[0191] If the outcome of the judgment formed at the step S14 indicatesthat the specific GOP (n) picture, at which the picked observed editpoint STP has been set, is not picture I3, on the other hand, the flowof the processing goes on to a step S17 at which the controller 7 formsa judgment as to whether or not the specific GOP (n) picture, at whichthe picked observed edit point STP has been set, is picture B4, B5 orP6.

[0192] If the outcome of the judgment formed at the step S17 indicatesthat the specific GOP (n) picture, at which the picked observed editpoint STP has been set, is picture B4, B5 or P6, the flow of theprocessing goes on to a step S18 at which the controller 7 determinespicture I3 pertaining to GOP (n) to be the preparatorily decoded picturefor the observed edit point STP. Then, the flow of the processing goeson to a step S19. At the step S19, the controller 7 computes the picturecount of the list of the preparatorily decoded pictures. In this case,the picture count is one. Since the picture count is one, which is thenumber of pictures on the list of preparatorily decoded picture I3, thecontroller 7 finds out that the preparatory decoding time is equal to aperiod of time it takes to decode one frame. Then, the flow of theprocessing goes back to the step S11 to repeat the processing describedabove. To be more specific, at this step S11, the controller 7 picks oneof edit points that are each described on the edit-point list as an INpoint as a new edit point STP not processed yet in thepreparatory-picture computation processing.

[0193] If the outcome of the judgment formed at the step S17 indicatesthat the specific GOP (n) picture, at which the picked observed editpoint STP has been set, is not picture B4, B5 or P6, on the other hand,the flow of the processing goes on to a step S20 at which the controller7 forms a judgment as to whether or not the specific GOP (n) picture, atwhich the picked observed edit point STP has been set, is picture B7, B8or P9.

[0194] If the outcome of the judgment formed at the step S20 indicatesthat the specific GOP (n) picture, at which the picked observed editpoint STP has been set, is picture B7, B8 or P9, the flow of theprocessing goes on to a step S21 at which the controller 7 determinespictures I3 and P6 pertaining to GOP (n) to be the preparatorily decodedpictures for the observed edit point STP. Then, the flow of theprocessing goes on to a step S22. At the step S22, the controller 7computes the picture count of the list of the preparatorily decodedpictures. In this case, the picture count is two. Since the picturecount is two, which is the number of pictures on the list ofpreparatorily decoded pictures I3 and P6, the controller 7 finds outthat the preparatory decoding time is equal to a period of time it takesto decode two frames. Then, the flow of the processing goes back to thestep S11 to repeat the processing described above. To be more specific,at this step S11, the controller 7 picks one of edit points that areeach described on the edit-point list as an IN point as a new edit pointSTP not processed yet in the preparatory-picture computation processing.

[0195] If the outcome of the judgment formed at the step S20 indicatesthat the specific GOP (n) picture, at which the picked observed editpoint STP has been set, is not picture B7, B8 or P9, on the other hand,the flow of the processing goes on to a step S23 at which the controller7 forms a judgment as to whether or not the specific GOP (n) picture, atwhich the picked observed edit point STP has been set, is picture B10,B11 or P12.

[0196] If the outcome of the judgment formed at the step S23 indicatesthat the specific GOP (n) picture, at which the picked observed editpoint STP has been set, is picture B10, B11 or P12, the flow of theprocessing goes on to a step S24 at which the controller 7 determinespictures I3, P6 and P9 pertaining to GOP (n) to be the preparatorilydecoded pictures for the observed edit point STP. Then, the flow of theprocessing goes on to a step S25. At the step S25, the controller 7computes the picture count of the list of the preparatorily decodedpictures. In this case, the picture count is three. Since the picturecount is three, which is the number of pictures on the list ofpreparatorily decoded pictures I3, P6 and P9, the controller 7 finds outthat the preparatory decoding time is equal to a period of time it takesto decode three frames. Then, the flow of the processing goes back tothe step S11 to repeat the processing described above. To be morespecific, at this step S11, the controller 7 picks one of edit pointsthat are each described on the edit-point list as an IN point as a newedit point STP not processed yet in the preparatory-picture computationprocessing.

[0197] If the outcome of the judgment formed at the step S23 indicatesthat the specific GOP (n) picture, at which the picked observed editpoint STP has been set, is not picture B10, B11 or P12, on the otherhand, the flow of the processing goes on to a step S26 at which thecontroller 7 determines pictures I3, P6, P9 and P12 pertaining to GOP(n) to be the preparatorily decoded pictures for the observed edit pointSTP. Then, the flow of the processing goes on to a step S27. At the stepS27, the controller 7 computes the picture count of the list of thepreparatorily decoded pictures. In this case, the picture count is four.Since the picture count is four, which is the number of pictures on thelist of preparatorily decoded pictures I3, P6, P9 and P12, thecontroller 7 finds out that the preparatory decoding time is equal to aperiod of time it takes to decode four frames. Then, the flow of theprocessing goes back to the step S11 to repeat the processing describedabove. To be more specific, at this step S11, the controller 7 picks oneof edit points that are each described on the edit-point list as an INpoint as a new edit point STP not processed yet in thepreparatory-picture computation processing.

[0198] It is to be noted that the execution of the preparatory-picturecomputation processing represented by the flowchart shown in FIG. 11 isended when the controller 7 no longer finds one of edit points that areeach described on the edit-point list as an IN point as a new edit pointSTP not processed yet in the preparatory-picture computation processing.

[0199]FIG. 12 is a diagram showing a typical configuration of anotherembodiment implementing the disc system, to which the present inventionis applied. Components of the other embodiment, which are identical withtheir respective counterparts employed in the embodiment shown in FIG.5, are denoted by the same reference numerals as the counterparts.Explanations of the components identical with their counterparts areomitted if unnecessary. In the case of the disc system shown in FIG. 2,the number of decoders employed in the decoding unit 4 is not limited totwo, namely, the decoders 4 ₁ and 4 ₂. Instead, the decoding unit 4includes k decoders 4 ₁, 4 ₂, — and 4 _(k). The rest is the same as theembodiment shown in FIG. 5. It is to be noted that, typically, thedecoders 4 _(k) (where k=1, 2, — and K) shown in FIG. 12 each have aone-time decoding process speed as is the case with the decoders 4 ₁ and4 ₂ shown in FIG. 5.

[0200] The disc system shown in FIG. 5 is identical with the disc systemshown in FIG. 12 for K=2. As described above, the shortest cut durationof the embodiment shown in FIG. 5 is equal to the period of time ittakes to display six frames. In the case of the embodiment shown in FIG.12, by increasing the number of decoders 4 ₁ to 4 _(k) composing thedecoding unit 4, that is, by setting K at a number greater than 2, theshortest cut duration can be made shorter than the period of time ittakes to display six frames.

[0201] To put it concretely, for example, K is set at 3, that is, thedecoding unit 4 includes three decoders 4 ₁, 4 ₂ and 4 ₃. In this case,the shortest cut duration can be reduced to a period of time it takes todisplay three frames.

[0202] Now, assume that an editing process has been carried out todisplay pictures B1, B2 and I3 pertaining to GOP (n) beginning at a timet_(a), then pictures B1, B2 and I3 pertaining to GOP (n+1) beginning ata time t_(b), then pictures B1, B2 and I3 pertaining to GOP (n+2)beginning at a time t_(c) and, finally, pictures pertaining to GOP (n+3)and subsequent GOPs beginning at a time t_(d) as shown in apicture-displaying order 261 of FIG. 13. In this case, as IN points,edit points are set at picture B1 pertaining to GOP (n) to be displayedat the time t_(a), picture B1 pertaining to GOP (n+1) to be displayed atthe time t_(b), picture B1 pertaining to GOP (n+2) to be displayed atthe time t_(c) and picture B1 pertaining to GOP (n+3) to be displayed atthe time t_(d).

[0203] It is to be noted that, in this case, the time t_(b) lags behindthe time t_(a) by a period of time it takes to display three frames, thetime t_(c) lags behind the time t_(b) by a period of time it takes todisplay three frames and the time t_(d) lags behind the time t_(c) by aperiod of time it takes to display three frames. Thus, in thepicture-displaying order 261 shown in FIG. 13, the shortest cut durationis a period of time it takes to display the three frames between thetimes t_(a) and t_(b) (or the three frames between the times t_(b) andt_(c) or the three frames between the times t_(c) and t_(d)).

[0204] In this case, first of all, pictures B1, B2 and I3 pertaining toGOP (n) must be displayed beginning at the time t_(a) with picture B1 atwhich an edit point has been set as an IN point. Thus, as describedearlier, the controller 7 drives a specific one of the three decoders 4₁ to 4 ₃ to decode pictures I3, P6, P9, P12 and P15 pertaining to GOP(n−1) immediately preceding GOP (n) and, then, pictures I3, B1 and B2pertaining to GOP (n) in accordance with the schedule shown on the firstline of FIG. 7 as shown in a picture-decoding order 262 of FIG. 13. Thespecific decoder is a decoder that is not carrying out a decodingprocess at the present time. For example, the decoders 4 ₁ is selectedas the specific decoder.

[0205] It is to be noted that, in the process to decode pictures I3, B1and B2 pertaining to GOP (n), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time t_(a) of picture B1. Thus, the process to decodepicture I3 pertaining to GOP (n−1) and leading ahead of picture B1pertaining to GOP (n) by seven pictures must be started before a timeleading ahead of the time t_(a) by a period of time it takes to displayseven pictures. In the picture-decoding order 262 shown in FIG. 13, atime t_(a−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n−1). Thus, the process to decode pictureI3 pertaining to GOP (n−1) is started at the time t_(a−7) whereas theprocess to decode picture B2 pertaining to GOP (n) is completed by atime t_(a+1) lagging behind the time t_(a) by a period of time it takesto display one picture. Picture B2 pertaining to GOP (n) is a picture tobe decoded last among pictures I3, B1 and B2 pertaining to GOP (n).

[0206] After the decoder 4 ₁ displays decoded pictures B1, B2 and I3pertaining to GOP (n), the time t_(b) is reached as shown in thepicture-displaying order 261 of FIG. 13. Thus, pictures B1, B2 and I3pertaining to GOP (n+1), which are to be displayed starting at the timet_(b), must be decoded and displayed since an edit point has been set atpicture B1 pertaining to GOP (n+1) as an IN point.

[0207] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the three decoders 4 ₁ to 4 ₃ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n)immediately preceding GOP (n+1) and, then, pictures I3, B1 and B2pertaining to GOP (n) in accordance with the schedule shown on the firstline of FIG. 7 as shown in a picture-decoding order 264 of FIG. 13. Thespecific decoder is a decoder that is not carrying out a decodingprocess at the present time. For example, the decoder 4 ₂ is selected asthe specific decoder.

[0208] It is to be noted that, in the process to decode pictures I3, B1and B2 pertaining to GOP (n+1), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time t_(b) of picture B1. Thus, the process to decodepicture I3 pertaining to GOP (n) and leading ahead of picture B1pertaining to GOP (n+1) by seven pictures must be started before a timeleading ahead of the time t_(b) by a period of time it takes to displayseven pictures. In the picture-decoding order 264 shown in FIG. 13, atime t_(b−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n). Thus, the process to decode picture I3pertaining to GOP (n) is started at the time t_(b−7) whereas the processto decode picture B2 pertaining to GOP (n+1) is completed by a timet_(b+1) lagging behind the time t_(b) by a period of time it takes todisplay one picture. Picture B2 pertaining to GOP (n+1) is a picture tobe decoded last among pictures I3, B1 and B2 pertaining to GOP (n+1).

[0209] After the decoder 4 ₂ displays decoded pictures B1, B2 and I3pertaining to GOP (n+1), the time t_(c) is reached as shown in thepicture-displaying order 261 of FIG. 13. Thus, pictures B1, B2 and I3pertaining to GOP (n+2), which are to be displayed starting at the timetc, must be decoded and displayed since an edit point has been set atpicture B1 pertaining to GOP (n+2) as an IN point.

[0210] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the three decoders 4 ₁ to 4 ₃ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n+1)immediately preceding GOP (n+2) and, then, pictures I3, B1 and B2pertaining to GOP (n+2) in accordance with the schedule shown on thefirst line of FIG. 7 as shown in a picture-decoding order 265 of FIG.13. The specific decoder is a decoder that is not carrying out adecoding process at the present time. In this case, the only remainingdecoder 4 ₃ is selected as the specific decoder.

[0211] It is to be noted that, in the process to decode pictures I3, B1and B2 pertaining to GOP (n+2), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time t_(c) of picture B1. Thus, the process to decodepicture I3 pertaining to GOP (n+1) and leading ahead of picture B1pertaining to GOP (n+2) by seven pictures must be started before a timeleading ahead of the time tc by a period of time it takes to displayseven pictures. In the picture-decoding order 265 shown in FIG. 13, atime t_(c−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n+1). Thus, the process to decode pictureI3 pertaining to GOP (n+1) is started at the time t_(c−7) whereas theprocess to decode picture B2 pertaining to GOP (n+2) is completed by atime t_(c+1) lagging behind the time tc by a period of time it takes todisplay one picture. Picture B2 pertaining to GOP (n+2) is a picture tobe decoded last among pictures I3, B1 and B2 pertaining to GOP (n+2).

[0212] After the decoder 4 ₃ displays decoded pictures B1, B2 and I3pertaining to GOP (n+2), the time t_(d) is reached as shown in thepicture-displaying order 261 of FIG. 13. Thus, pictures B1, B2 and I3pertaining to GOP (n+3), which are to be displayed starting at the timet_(d), and the subsequent pictures, must be decoded and displayed sincean edit point has been set at picture B1 pertaining to GOP (n+3) as anIN point.

[0213] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the 3 decoders 4 ₁ to 4₃ to decodepictures I3, P6, P9, P12 and P15 pertaining to GOP (n+2) immediatelypreceding GOP (n+3) in order to decode picture B1 pertaining to GOP(n+3) in accordance with the schedule shown on the first line of FIG. 7as shown in a picture-decoding order 263 of FIG. 13.

[0214] It is to be noted that, in the process to decode picturespertaining to GOP (n+3), the processing to decode picture B1, at whichan edit point has been set as an IN point, must be completed by thedisplay time t_(d) of picture B1. Thus, the process to decode picture I3pertaining to GOP (n+2) and leading ahead of picture B1 pertaining toGOP (n+3) by seven pictures must be started before a time leading aheadof the time t_(d) by a period of time it takes to display sevenpictures. In the picture-decoding order 263 shown in FIG. 13, a timet_(d−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n+2).

[0215] By the way, with the timing of the time t_(d−7), while thedecoders 4 ₂ and 4 ₃ are each still carrying out a decoding process asis obvious from respectively the picture-decoding orders 264 and 265shown in FIG. 13, the decoders 4 ₁ has completed its decoding process atthe time t_(a+1) leading ahead of the time t_(d−7) by a period of timeit takes to display one picture as shown in the picture-decoding orders262 and 263 of FIG. 13. Thus, at the time t_(d−7), the decoders 4 ₁ isavailable for a decoding process. For this reason, the controller 7drives the decoders 4 ₁ to decode pictures I3, P6, P9, P12 and P15pertaining to GOP (n+2) and, then, pictures I3, B1 and B2 pertaining toGOP (n+3).

[0216] As is obvious from the above description, if the shortest cutduration is equal to a period of time it takes to display three frames,there is no case in which the decoders 4 ₁, 4 ₂ and 4 ₃ must decode aplurality of pictures at the same time.

[0217] Thus, by designing the decoding unit 4 to include the threedecoders 4 ₁, 4 ₂ and 4 ₃, the shortest cut duration can be reduced to aperiod of time it takes to display three frames. That is to say, theembodiment employing three decoders allows the shortest cut duration tobe reduced to a period shorter than the embodiment wherein the decodingunit 4 includes only the two decoders 4 ₁ and 4 ₂ as shown in FIG. 5. Asa result, the freedom of editing can be further improved.

[0218] The following description explains an implementation of theembodiment realizing the disc system as shown in FIG. 12 wherein theshortest cut duration can be further reduced to a period of time ittakes to display two frames by designing the decoding unit 4 to includefour decoders 4 ₁, 4 ₂, 4 ₃ and 4 ₄, that is, by setting the value of Kat 4.

[0219] To put it in detail, now, assume that an editing process has beencarried out to display pictures B1 and B2 pertaining to GOP (n)beginning at a time t_(a), then pictures B1 and B2 pertaining to GOP(n+1) beginning at a time t_(b), then pictures B1 and B2 pertaining toGOP (n+2) beginning at a time t_(c), then pictures B1 and B2 pertainingto GOP (n+3) beginning at a time t_(d) and, finally, pictures pertainingto GOP (n+4) and subsequent GOPs beginning at a time t_(e) as shown in apicture-displaying order 271 of FIG. 14. In this case, as IN points,edit points are set at picture B1 pertaining to GOP (n) to be displayedat the time t_(a), picture B1 pertaining to GOP (n+1) to be displayed atthe time t_(b), picture B1 pertaining to GOP (n+2) to be displayed atthe time t_(c), picture B1 pertaining to GOP (n+3) to be displayed atthe time t_(d) and picture B1 pertaining to GOP (n+4) to be displayed atthe time t_(e).

[0220] It is to be noted that, in this case, the time t_(b) lags behindthe time t_(a) by a period of time it takes to display two frames, thetime t_(c) lags behind the time t_(b) by a period of time it takes todisplay two frames, the time t_(d) lags behind the time tc by a periodof time it takes to display two frames and the time t_(e) lags behindthe time t_(d) by a period of time it takes to display two frames. Thus,in the picture-displaying order 271 shown in FIG. 14, the shortest cutduration is a period of time it takes to display the two frames betweenthe times t_(a) and t_(b) (or the two frames between the times t_(b) andt_(c), the two frames between the times t_(c) and t_(d) or the twoframes between the times t_(d) and t_(e)).

[0221] In this case, first of all, pictures B1 and B2 pertaining to GOP(n) must be displayed beginning at the time t_(a) with picture B1 atwhich an edit point has been set as an IN point. Thus, as describedearlier, the controller 7 drives a specific one of the four decoders 4 ₁to 4 ₄ to decode pictures I3, P6, P9, P12 and P15 pertaining to GOP(n−1) immediately preceding GOP (n) and, then, pictures I3, B1 and B2pertaining to GOP (n) in accordance with the schedule shown on the firstline of FIG. 7 as shown in a picture-decoding order 272 of FIG. 14. Eventhough picture I3 pertaining to GOP (n) is not to be displayed, pictureI3 is referenced in decoding pictures B1 and B2 pertaining to the samegroup. Thus, picture I3 pertaining to GOP (n) must also be decoded. Thespecific decoder is a decoder that is not carrying out a decodingprocess at the present time. For example, the decoder 4 ₁ is selected asthe specific decoder.

[0222] It is to be noted that, in the process to decode pictures I3, B1and B2 pertaining to GOP (n), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time t_(a) of picture B1. Thus, the process to decodepicture I3 pertaining to GOP (n−1) and leading ahead of picture B1pertaining to GOP (n) by seven pictures must be started before a timeleading ahead of the time t₈ by a period of time it takes to displayseven pictures. In the picture-decoding order 272 shown in FIG. 14, atime t_(a−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n−1). Thus, the process to decode pictureI3 pertaining to GOP (n−1) is started at the time t_(a−7) whereas theprocess to decode picture B2 pertaining to GOP (n) is completed by atime t_(a+1) lagging behind the time t_(a) by a period of time it takesto display one picture. Picture B2 pertaining to GOP (n) is a picture tobe decoded last among pictures I3, B1 and B2 pertaining to GOP (n).

[0223] After the decoders 4 ₁ decodes pictures I3, B1, and B2 pertainingto GOP (n) and displays only pictures B1 and B2 pertaining to the samegroup, the time t_(b) is reached as shown in the picture-displayingorder 271 of FIG. 14. Thus, pictures B1, B2 and I3 pertaining to GOP(n+1) must be decoded in order to display pictures B1 and B2 pertainingto the same group, starting at the display time t_(b) of picture B1pertaining to the same group since an edit point has been set at pictureB1 as an IN point. Even though picture I3 pertaining to GOP (n+1) is notto be displayed, picture I3 is referenced in decoding pictures B1 and B2pertaining to the same group. Thus, picture I3 pertaining to GOP (n+1)must also be decoded.

[0224] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the four decoders 4 ₁ to 4 ₄ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n)immediately preceding GOP (n+1) and, then, pictures I3, B1 and B2pertaining to GOP (n+1) in accordance with the schedule shown on thefirst line of FIG. 7 as shown in a picture-decoding order 273 of FIG.14. The specific decoder is a decoder that is not carrying out adecoding process at the present time. For example, the decoder 4 ₂ isselected as the specific decoder.

[0225] It is to be noted that, in the process to decode pictures I3, B1and B2 pertaining to GOP (n+1), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time t_(b) of picture B1. Thus, the process to decodepicture I3 pertaining to GOP (n) and leading ahead of picture B1pertaining to GOP (n+1) by seven pictures must be started before a timeleading ahead of the time t_(b) by a period of time it takes to displayseven pictures. In the picture-decoding order 274 shown in FIG. 14, atime t_(b−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n). Thus, the process to decode picture I3pertaining to GOP (n) is started at the time t_(b−7) whereas the processto decode picture B2 pertaining to GOP (n+1) is completed by a timet_(b+1) lagging behind the time t_(b) by a period of time it takes todisplay one picture. Picture B2 pertaining to GOP (n+1) is a picture tobe decoded last among pictures I3, B1 and B2 pertaining to GOP (n+1).

[0226] After the decoder 4 ₂ decodes pictures I3, B1 and B2 pertainingto GOP (n) and displays only pictures B1 and B2 pertaining to the samegroup, the time t_(c) is reached as shown in the picture-displayingorder 271 of FIG. 14. Thus, pictures B1, B2 and I3 pertaining to GOP(n+2) must be decoded in order to display pictures B1 and B2 pertainingto the same group, starting at the display time t_(c) of picture B1pertaining to the same group since an edit point has been set at pictureB1 pertaining to GOP (n+2) as an IN point. Even though picture I3pertaining to GOP (n+2) is not to be displayed, picture I3 is referencedin decoding pictures B1 and B2 pertaining to the same group. Thus,picture I3 pertaining to GOP (n+2) must also be decoded.

[0227] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the four decoders 4 ₁ to 4 ₄ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n+1)immediately preceding GOP (n+2) and, then, pictures I3, B1 and B2pertaining to GOP (n+2) in accordance with the schedule shown on thefirst line of FIG. 7 as shown in a picture-decoding order 274 of FIG.14. The specific decoder is a decoder that is not carrying out adecoding process at the present time. For example, the decoder 4 ₃ isselected as the specific decoder.

[0228] It is to be noted that, in the process to decode pictures I3, B1and B2 pertaining to GOP (n+2), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time tc of picture B1. Thus, the process to decode pictureI3 pertaining to GOP (n+1) and leading ahead of picture B1 pertaining toGOP (n+2) by seven pictures must be started before a time leading aheadof the time t_(c) by a period of time it takes to display sevenpictures. In the picture-decoding order 274 shown in FIG. 14, a timet_(c−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n+1). Thus, the process to decode pictureI3 pertaining to GOP (n+1) is started at the time t_(c−7) whereas theprocess to decode picture B2 pertaining to GOP (n+2) is completed by atime t_(c+1) lagging behind the time t_(c) by a period of time it takesto display one picture. Picture B2 pertaining to GOP (n+2) is a pictureto be decoded last among pictures I3, B1 and B2 pertaining to GOP (n+2).

[0229] After the decoder 4 ₃ decodes pictures I3, B1 and B2 pertainingto GOP (n+2) and displays only pictures B1 and B2 pertaining to the samegroup, the time t_(d) is reached as shown in the picture-displayingorder 271 of FIG. 14. Thus, pictures B1, B2 and I3 pertaining to GOP(n+3) must be decoded in order to display pictures B1 and B2 pertainingto the same group, starting at the display time t_(d) of picture B1pertaining to the same group since an edit point has been set at pictureB1 as an IN point. Even though picture I3 pertaining to GOP (n+3) is notto be displayed, picture I3 is referenced in decoding pictures B1 and B2pertaining to the same group. Thus, picture I3 pertaining to GOP (n+3)must also be decoded.

[0230] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the four decoders 4 ₁ to 4 ₄ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n+2)immediately preceding GOP (n+3) and, then, pictures I3, B1 and B2pertaining to GOP (n+3) in accordance with the schedule shown on thefirst line of FIG. 7 as shown in a picture-decoding order 275 of FIG.14. The specific decoder is a decoder that is not carrying out adecoding process at the present time. In this case, the only remainingdecoder 4 ₄ is selected as the specific decoder.

[0231] It is to be noted that, in the process to decode pictures I3, B1and B2 pertaining to GOP (n+3), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time t_(d) of picture B1. Thus, the process to decodepicture I3 pertaining to GOP (n+2) and leading ahead of picture B1pertaining to GOP (n+3) by seven pictures must be started before a timeleading ahead of the time t_(d) by a period of time it takes to displayseven pictures. In the picture-decoding order 275 shown in FIG. 14, atime t_(d−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n+2). Thus, the process to decode pictureI3 pertaining to GOP (n+2) is started at the time t_(d−7) whereas theprocess to decode picture B2 pertaining to GOP (n+3) is completed by atime t_(d+1) lagging behind the time t_(d) by a period of time it takesto display one picture. Picture B2 pertaining to GOP (n+3) is a pictureto be decoded last among pictures I3, B1 and B2 pertaining to GOP (n+3).

[0232] After the decoder 4 ₄ decodes pictures I3, B1 and B2 pertainingto GOP (n+3) and displays only pictures B1 and B2 pertaining to the samegroup, the time t_(e) is reached as shown in the picture-displayingorder 271 of FIG. 14. Thus, pictures B1, B2 and I3 pertaining to GOP(n+4) and subsequent pictures must be decoded, starting at the displaytime t_(e) of picture B1 pertaining to the same group since an editpoint has been set at picture B1 pertaining to GOP (n+4) as an IN point.

[0233] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the four decoders 4 ₁ to 4 ₄ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n+3)immediately preceding GOP (n+4) in order to decode picture B1 pertainingto GOP (n+4) in accordance with the schedule shown on the first line ofFIG. 7 as shown in the picture-decoding order 272 of FIG. 14.

[0234] It is to be noted that, in the process to decode picturespertaining to GOP (n+4), the processing to decode picture B1, at whichan edit point has been set as an IN point, must be completed by thedisplay time t_(e) of picture B1. Thus, the process to decode picture I3pertaining to GOP (n+3) and leading ahead of picture B1 pertaining toGOP (n+4) by seven pictures must be started before a time leading aheadof the time t_(e) by a period of time it takes to display sevenpictures. In the picture-decoding order 272 shown in FIG. 14, a timet_(e−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n+3).

[0235] By the way, with the timing of the time t_(e−7), while thedecoders 4 ₂, 4 ₃ and 4 ₄ are each still carrying out a decoding processas is obvious from respectively the picture-decoding orders 273, 274 and275 shown in FIG. 14, the decoders 4 ₁ has completed its decodingprocess at the time t_(a+1), coinciding with the time t_(e−7) as shownin the picture-decoding order 272 of FIG. 14. Thus, at the time t_(e−7),the decoders 4 ₁ is available for a decoding process.

[0236] For this reason, the controller 7 drives the decoders 4 ₁ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n+3) and,then, pictures I3, B1 and B2 pertaining to GOP (n+4) as shown in thepicture-decoding order 272 of FIG. 14.

[0237] As is obvious from the above description, even the shortest cutduration is equal to a period of time it takes to display two frames,there is no case in which the decoders 4 ₁, 4 ₂, 4 ₃ and 4 ₄ must decodea plurality of pictures at the same time. Thus, by designing thedecoding unit 4 to include the four decoders 4 ₁, 4 ₂, 4 ₃ and 4 ₄, theshortest cut duration can be reduced to a period of time it takes todisplay two frames. That is to say, the embodiment employing fourdecoders allows the shortest cut duration to be reduced to a periodshorter than the embodiment wherein the decoding unit 4 includes onlythe three decoders 4 ₁, 4 ₂ and 4 ₃ as described earlier by referring toFIG. 13. As a result, the freedom of editing can be further improved.

[0238] The following description explains an implementation of theembodiment realizing the disc system as shown in FIG. 12 wherein theshortest cut duration can be further reduced to a period of time ittakes to display one frame by designing the decoding unit 4 to compriseseven decoders 4 ₁, 4 ₂, 4 ₃, 4 ₄, 4 ₅, 4 ₆ and 4 ₇, that is, by settingthe value of K at 7.

[0239] To put it in detail, now, assume that an editing process has beencarried out to display picture B1 pertaining to GOP (n) beginning at atime t_(a), then picture B1 pertaining to GOP (n+1) beginning at a timet_(b), then picture B1 pertaining to GOP (n+2) beginning at a timet_(c), then pictures B1 and B2 pertaining to GOP (n+3) beginning at atime t_(d), then pictures B1 and B2 pertaining to GOP (n+4) beginning ata time te, then pictures B1 and B2 pertaining to GOP (n+5) beginning ata time tf, then pictures B1 and B2 pertaining to GOP (n+6) beginning ata time t_(g) and, finally, pictures pertaining to GOP (n+7) andsubsequent GOPs beginning at a time th as shown in a picture-displayingorder 281 of FIG. 15. In this case, as IN points, edit points are set atpicture B1 pertaining to GOP (n) to be displayed at the time t_(a),picture B1 pertaining to GOP (n+1) to be displayed at the time t_(b),picture B1 pertaining to GOP (n+2) to be displayed at the time t_(c),picture B1 pertaining to GOP (n+3) to be displayed at the time t_(d), B1pertaining to GOP (n+4) to be displayed at the time t_(e), B1 pertainingto GOP (n+5) to be displayed at the time t_(f), B1 pertaining to GOP(n+6) to be displayed at the time t_(g) and picture B1 pertaining to GOP(n+7) to be displayed at the time t_(h).

[0240] It is to be noted that, in this case, the time t_(b) lags behindthe time t_(a) by a period of time it takes to display one frame, thetime t_(c) lags behind the time t_(b) by a period of time it takes todisplay one frame, the time t_(d) lags behind the time t_(c) by a periodof time it takes to display one frame, the time t_(e) lags behind thetime t_(d) by a period of time it takes to display one frame, the timet_(f) lags behind the time t_(e) by a period of time it takes to displayone frame, the time t_(g) lags behind the time t_(f) by a period of timeit takes to display one frame and the time t_(h) lags behind the timet_(g) by a period of time it takes to display one frame. Thus, in thepicture-displaying order 281 shown in FIG. 15, the shortest cut durationis a period of time it takes to display the one frame between the timest_(a) and t_(b) (or the one frame between the times t_(b) and t_(c), theone frame between the times t_(c) and t_(d), the one frame between thetimes t_(d) and te, the one frame between the times t_(e) and tf, theone frame between the times t_(f) and t_(g) or the one frame between thetimes t_(q) and t_(h)).

[0241] In this case, first of all, pictures B1 and I3 pertaining to GOP(n) must be displayed beginning at the time t_(a) with picture B1 atwhich an edit point has been set as an IN point. Thus, as describedearlier, the controller 7 drives a specific one of the seven decoders 4₁ to 4 ₇ to decode pictures I3, P6, P9, P12 and P15 pertaining to GOP(n−1) immediately preceding GOP (n) and, then, pictures I3 and B1pertaining to GOP (n) in accordance with the schedule shown on the firstline of FIG. 7 as shown in a picture-decoding order 282 of FIG. 15. Eventhough picture I3 pertaining to GOP (n) is not to be displayed, pictureI3 is referenced in decoding pictures B1 and B2 pertaining to the samegroup. Thus, picture I3 pertaining to GOP (n) must also be decoded. Thespecific decoder is a decoder that is not carrying out a decodingprocess at the present time. For example, the decoder 4 ₁ is selected asthe specific decoder.

[0242] It is to be noted that, in the process to decode pictures I3 andB1 pertaining to GOP (n), the processing to decode picture B1, at whichan edit point has been set as an IN point, must be completed by thedisplay time ta of picture B1. Thus, the process to decode picture I3pertaining to GOP (n−1) and leading ahead of picture B1 pertaining toGOP (n) by seven pictures must be started before a time leading ahead ofthe time t_(a) by a period of time it takes to display seven pictures.In the picture-decoding order 282 shown in FIG. 15, a time t_(a−7) isdetermined to be the time to start the process to decode picture I3pertaining to GOP (n−1). Thus, the process to decode picture I3pertaining to GOP (n−1) is started at the time t_(a−7) whereas theprocess to decode picture B1 pertaining to GOP (n) is completed by thetime ta. Picture B1 pertaining to GOP (n) is a picture to be decodedlast among pictures I3 and B1 pertaining to GOP (n).

[0243] After the decoders 4 ₁ decodes pictures I3 and B1 pertaining toGOP (n) and displays only picture B1 pertaining to the same group, thetime t_(b) is reached as shown in the picture-displaying order 281 ofFIG. 15. Thus, pictures B1 and I3 pertaining to GOP (n+1) must bedecoded in order to display picture B1 pertaining to the same group,starting at the display time t_(b) of picture B1 pertaining to the samegroup since an edit point has been set at picture B1 as an IN point.Even though picture I3 pertaining to GOP (n+1) is not to be displayed,picture I3 is referenced in decoding picture B1 pertaining to the samegroup. Thus, picture I3 pertaining to GOP (n+1) must also be decoded.

[0244] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the seven decoders 4 ₁ to 4 ₇ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n)immediately preceding GOP (n+1) and, then, pictures I3 and B1 pertainingto GOP (n+1) in accordance with the schedule shown on the first line ofFIG. 7 as shown in a picture-decoding order 283 of FIG. 15. The specificdecoder is a decoder that is not carrying out a decoding process at thepresent time. For example, the decoder 4 ₂ is selected as the specificdecoder.

[0245] It is to be noted that, in the process to decode pictures I3 andB1 pertaining to GOP (n+1), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time t_(b) of picture B1. Thus, the process to decodepicture I3 pertaining to GOP (n) and leading ahead of picture B1pertaining to GOP (n+1) by seven pictures must be started before a timeleading ahead of the time t_(b) by a period of time it takes to displayseven pictures. In the picture-decoding order 284 shown in FIG. 15, atime t_(b−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n). Thus, the process to decode picture I3pertaining to GOP (n) is started at the time t_(b−7) whereas the processto decode picture B1 pertaining to GOP (n+1) is completed by the timet_(b). Picture B1 pertaining to GOP (n+1) is a picture to be decodedlast among pictures I3 and B1 pertaining to GOP (n+1).

[0246] After the decoder 4 ₂ decodes pictures I3 and B1 pertaining toGOP (n+1) and displays only picture B1 pertaining to the same group, thetime tc is reached as shown in the picture-displaying order 281 of FIG.15. Thus, pictures B1 and I3 pertaining to GOP (n+2) must be decoded inorder to display picture B1 pertaining to the same group, starting atthe display time t_(c) of picture B1 pertaining to the group since anedit point has been set at picture B1 as an IN point. Even thoughpicture I3 pertaining to GOP (n+2) is not to be displayed, picture I3 isreferenced in decoding picture B1 pertaining to the same group. Thus,picture I3 pertaining to GOP (n+2) must also be decoded.

[0247] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the seven decoders 4 ₁ to 4 ₇ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n+1)immediately preceding GOP (n+2) and, then, pictures I3 and B1 pertainingto GOP (n+2) in accordance with the schedule shown on the first line ofFIG. 7 as shown in a picture-decoding order 284 of FIG. 15. The specificdecoder is a decoder that is not carrying out a decoding process at thepresent time. For example, the decoder 4 ₃ is selected as the specificdecoder.

[0248] It is to be noted that, in the process to decode pictures I3 andB1 pertaining to GOP (n+2), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time t_(c) of picture B1. Thus, the process to decodepicture I3 pertaining to GOP (n+1) and leading ahead of picture B1pertaining to GOP (n+2) by seven pictures must be started before a timeleading ahead of the time tc by a period of time it takes to displayseven pictures. In the picture-decoding order 284 shown in FIG. 15, atime t_(c−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n+1). Thus, the process to decode pictureI3 pertaining to GOP (n+1) is started at the time t_(c−7) whereas theprocess to decode picture B1 pertaining to GOP (n+2) is completed by thetime t_(c). Picture B1 pertaining to GOP (n+2) is a picture to bedecoded last among pictures I3 and B1 pertaining to GOP (n+2).

[0249] After the decoder 4 ₃ decodes pictures I3 and B1 pertaining toGOP (n+2) and displays only picture B1 pertaining to the same group, thetime t_(d) is reached as shown in the picture-displaying order 281 ofFIG. 15. Thus, pictures B1 and I3 pertaining to GOP (n+3) must bedecoded in order to display picture B1 pertaining to the same group,starting at the display time t_(d) of picture B1 pertaining to the groupsince an edit point has been set at picture B1 pertaining to GOP (n+3)as an IN point. Even though picture I3 pertaining to GOP (n+3) is not tobe displayed, picture I3 is referenced in decoding picture B1 pertainingto the same group. Thus, picture I3 pertaining to GOP (n+3) must also bedecoded.

[0250] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the seven decoders 4 ₁ to 4 ₇ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n+2)immediately preceding GOP (n+3) and, then, pictures I3 and B1 pertainingto GOP (n+3) in accordance with the schedule shown on the first line ofFIG. 7 as shown in a picture-decoding order 285 of FIG. 15. The specificdecoder is a decoder that is not carrying out a decoding process at thepresent time. For example, the decoder 4 ₄ is selected as the specificdecoder.

[0251] It is to be noted that, in the process to decode pictures I3 andB1 pertaining to GOP (n+3), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time t_(d) of picture B1. Thus, the process to decodepicture I3 pertaining to GOP (n+2) and leading ahead of picture B1pertaining to GOP (n+3) by seven pictures must be started before a timeleading ahead of the time t_(d) by a period of time it takes to displayseven pictures. In the picture-decoding order 285 shown in FIG. 15, atime t_(d−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n+2). Thus, the process to decode pictureI3 pertaining to GOP (n+2) is started at the time t_(d−7) whereas theprocess to decode picture B1 pertaining to GOP (n+3) is completed by thetime t_(d). Picture B1 pertaining to GOP (n+3) is a picture to bedecoded last among pictures I3 and B1 pertaining to GOP (n+3).

[0252] After the decoder 4 ₄ decodes pictures I3 and B1 pertaining toGOP (n+3) and displays only picture B1 pertaining to the same group, thetime t_(e) is reached as shown in the picture-displaying order 281 ofFIG. 15. Thus, pictures B1 and I3 pertaining to GOP (n+4) must bedecoded in order to display picture B1 pertaining to the same group,starting at the display time t_(e) of picture B1 pertaining to the groupsince an edit point has been set at picture B1 pertaining to GOP (n+4)as an IN point. Even though picture I3 pertaining to GOP (n+4) is not tobe displayed, picture I3 is referenced in decoding picture B1 pertainingto the same group. Thus, picture I3 pertaining to GOP (n+4) must also bedecoded.

[0253] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the seven decoders 4 ₁ to 4 ₇ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n+3)immediately preceding GOP (n+4) and, then, pictures I3 and B1 pertainingto GOP (n+4) in accordance with the schedule shown on the first line ofFIG. 7 as shown in a picture-decoding order 286 of FIG. 15. The specificdecoder is a decoder that is not carrying out a decoding process at thepresent time. For example, the decoder 4 ₅ is selected as the specificdecoder.

[0254] It is to be noted that, in the process to decode pictures I3 andB1 pertaining to GOP (n+4), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time t_(e) of picture B1. Thus, the process to decodepicture I3 pertaining to GOP (n+3) and leading ahead of picture B1pertaining to GOP (n+4) by seven pictures must be started before a timeleading ahead of the time t_(e) by a period of time it takes to displayseven pictures. In the picture-decoding order 286 shown in FIG. 15, atime t_(e−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n+3). Thus, the process to decode pictureI3 pertaining to GOP (n+3) is started at the time te-7 whereas theprocess to decode picture B1 pertaining to GOP (n+4) is completed by thetime t_(e). Picture B1 pertaining to GOP (n+4) is a picture to bedecoded last among pictures I3 and B1 pertaining to GOP (n+3).

[0255] After the decoder 4 ₅ decodes pictures I3 and B1 pertaining toGOP (n+4) and displays only picture B1 pertaining to the same group, thetime t_(f) is reached as shown in the picture-displaying order 281 ofFIG. 15. Thus, pictures B1 and I3 pertaining to GOP (n+5) must bedecoded in order to display picture B1 pertaining to the same group,starting at the display time t_(f) of picture B1 pertaining to the groupsince an edit point has been set at picture B1 pertaining to GOP (n+5)as an IN point. Even though picture I3 pertaining to GOP (n+5) is not tobe displayed, picture I3 is referenced in decoding picture B1 pertainingto the same group. Thus, picture I3 pertaining to GOP (n+5) must also bedecoded.

[0256] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the seven decoders 4 ₁ to 4 ₇ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n+4)immediately preceding GOP (n+5) and, then, pictures I3 and B1 pertainingto GOP (n+5) in accordance with the schedule shown on the first line ofFIG. 7 as shown in a picture-decoding order 287 of FIG. 15. The specificdecoder is a decoder that is not carrying out a decoding process at thepresent time. For example, the decoder 4 ₆ is selected as the specificdecoder.

[0257] It is to be noted that, in the process to decode pictures I3 andB1 pertaining to GOP (n+5), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time t_(f) of picture B1. Thus, the process to decodepicture I3 pertaining to GOP (n+4) and leading ahead of picture B1pertaining to GOP (n+5) by seven pictures must be started before a timeleading ahead of the time t_(f) by a period of time it takes to displayseven pictures. In the picture-decoding order 287 shown in FIG. 15, atime t_(f−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n+4). Thus, the process to decode pictureI3 pertaining to GOP (n+4) is started at the time t_(f−7) whereas theprocess to decode picture B1 pertaining to GOP (n+5) is completed by thetime t_(f). Picture B1 pertaining to GOP (n+5) is a picture to bedecoded last among pictures I3 and B1 pertaining to GOP (n+5).

[0258] After the decoder 4 ₆ decodes pictures I3 and B1 pertaining toGOP (n+5) and displays only picture B1 pertaining to the same group, thetime t_(g) is reached as shown in the picture-displaying order 281 ofFIG. 15. Thus, pictures B1 and I3 pertaining to GOP (n+6) must bedecoded in order to display picture B1 pertaining to the same group,starting at the display time t_(g) of picture B1 pertaining to the groupsince an edit point has been set at picture B1 pertaining to GOP (n+6)as an IN point. Even though picture I3 pertaining to GOP (n+6) is not tobe displayed, picture I3 is referenced in decoding picture B1 pertainingto the same group. Thus, picture I3 pertaining to GOP (n+6) must also bedecoded.

[0259] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the seven decoders 4 ₁ to 4 ₇ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n+5)immediately preceding GOP (n+6) and, then, pictures I3 and B1 pertainingto GOP (n+6) in accordance with the schedule shown on the first line ofFIG. 7 as shown in a picture-decoding order 288 of FIG. 15. The specificdecoder is a decoder that is not carrying out a decoding process at thepresent time. In this case, the only remaining decoder 4 ₇ is selectedas the specific decoder.

[0260] It is to be noted that, in the process to decode pictures I3 andB1 pertaining to GOP (n+6), the processing to decode picture B1, atwhich an edit point has been set as an IN point, must be completed bythe display time t_(g) of picture B1. Thus, the process to decodepicture I3 pertaining to GOP (n+5) and leading ahead of picture B1pertaining to GOP (n+6) by seven pictures must be started before a timeleading ahead of the time t_(g) by a period of time it takes to displayseven pictures. In the picture-decoding order 288 shown in FIG. 15, atime t_(g−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n+5). Thus, the process to decode pictureI3 pertaining to GOP (n+5) is started at the time t_(g−7) whereas theprocess to decode picture B1 pertaining to GOP (n+6) is completed by thetime tg. Picture B1 pertaining to GOP (n+6) is a picture to be decodedlast among pictures I3 and B1 pertaining to GOP (n+6).

[0261] After the decoder 4 ₇ decodes pictures I3 and B1 pertaining toGOP (n+6) and displays only picture B1 pertaining to the same group, thetime t_(h) is reached as shown in the picture-displaying order 281 ofFIG. 15. Thus, pictures B1, B2 and I3 pertaining to GOP (n+7) andsubsequent pictures must be decoded, starting at the display time t_(h)of picture B1 pertaining to the group since an edit point has been setat picture B1 pertaining to GOP (n+7) as an IN point.

[0262] For the reason described above, as described earlier, thecontroller 7 drives a specific one of the seven decoders 4, to 4 ₇ todecode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n+6)immediately preceding GOP (n+7) in order to decode picture B1 pertainingto GOP (n+7) in accordance with the schedule shown on the first line ofFIG. 7 as shown in the picture-decoding order 282 of FIG. 15. Thespecific decoder is a decoder that is not carrying out a decodingprocess at the present time. In this case, the decoders 4 ₁ is againselected as the specific decoder for a reason described later.

[0263] It is to be noted that, in the process to decode picturespertaining to GOP (n+7), the processing to decode picture B1, at whichan edit point has been set as an IN point, must be completed by thedisplay time t_(h) of picture B1. Thus, the process to decode picture I3pertaining to GOP (n+6) and leading ahead of picture B1 pertaining toGOP (n+7) by seven pictures must be started before a time leading aheadof the time t_(h) by a period of time it takes to display sevenpictures. In the picture-decoding order 282 shown in FIG. 15, a timet_(h−7) is determined to be the time to start the process to decodepicture I3 pertaining to GOP (n+6).

[0264] By the way, with the timing of the time t_(h−7), while thedecoders 4 ₂ to 4 ₇ are each still carrying out a decoding process as isobvious from respectively the picture-decoding orders 283 to 288 shownin FIG. 15, the decoders 4 ₁ has completed its decoding process at thetime ta coinciding with the time t_(h−7) as shown in thepicture-decoding order 282 of FIG. 15.

[0265] Thus, at the time t_(h−7), the decoder 4 ₁ is available for adecoding process. For this reason, the controller 7 drives the decoders4 ₁ to decode pictures I3, P6, P9, P12 and P15 pertaining to GOP (n+6)and, then, pictures I3 and B1 pertaining to GOP (n+7) as shown in thepicture-decoding order 282 shown in FIG. 15.

[0266] As is obvious from the above description, with the decoding unit4 designed to include seven decoders 4 ₁ to 4 ₇, there is no case inwhich the decoders 4 ₁ to 4 ₇ must decode a plurality of pictures at thesame time even if the shortest cut duration is reduced to a period oftime it takes to display one frame. Thus, by designing the decoding unit4 to include the seven decoders 4 ₁ to 4 ₇, the shortest cut durationcan be reduced to a period of time it takes to display one frame. As aresult, an editing process can be carried out without restrictionscaused by the shortest cut duration.

[0267]FIG. 16 is a diagram showing a relation between the number ofdecoders 4 ₁ to 4 _(k) (K) composing the decoding unit 4 and theshortest cut duration. As shown in FIG. 16, if the number of decoders 4₁ to 4 _(k) (K) is set at 2, the shortest cut duration is equal to aperiod of time it takes to display six frames. If the number of decoders4 ₁ to 4 _(k) (K) is set at 3, the shortest cut duration is equal to aperiod of time it takes to display three frames. If the number ofdecoders 4 ₁ to 4 _(k) (K) is set at 3, 4 or 5, the shortest cutduration is equal to a period of time it takes to display two frames. Ifthe number of decoders 4 ₁ to 4 _(k) (K) is set at 7 or a greaternumber, the shortest cut duration is equal to a period of time it takesto display one frame.

[0268] It is to be noted that the relation shown in FIG. 16 isestablished between the number of decoders 4 ₁ to 4 _(k) (K) composingthe decoding unit 4 and the shortest cut duration for the decoders 4 ₁to 4 _(k) (K) of the decoding unit 4 each having a one-time decodingprocess speed. If the decoders 4 ₁ to 4 _(k) composing the decoding unit4 each have an L-time decoding process speed where L is a positivenumber), the shortest cut duration can be reduced to a period of time ittakes to display one frame by composing the decoding unit 4 of at least7/L decoders 4 ₁, 4 ₂ and so on. In this case, an editing process can becarried out without restrictions caused by the shortest cut duration.

[0269] Next, the reproduction process carried out by the disc systemshown in FIG. 12 is further explained by referring to a flowchart shownin FIG. 17.

[0270] When the user operates the operation unit 8 to start a process toreproduce a result of edit processing of an MPEG stream in accordancewith an edit-point list, the operation unit 8 outputs areproduction-start operation signal, which is an operation signal makinga request for a start of a reproduction process, to the controller 7.

[0271] When receiving the reproduction-start operation signal from theoperation unit 8 at a step S31, the controller 7 issues a request for anedit-point list to the disc drive 2. At this request, the disc drive 2reads out the edit-point list from the optical disc 1 and then outputsthe list to the bus 3. Then, the controller 7 receives the edit-pointlist from the bus 3. Subsequently, at the next step S32, the controllerdetects all IN and OUT points included on the edit-point list and makesa table of edit points. The table of edit points is properly referred tohereafter as an edit-point table.

[0272] It is to be noted that, in the edit-point table, edit points aredescribed in a display-time order.

[0273] Then, at the next step S33, the controller 7 carries out aprocess to find preparatorily decoded pictures for each of the editpoints, which is described in the edit-point table as an IN point. Theprocess to find preparatorily decoded pictures has been explained beforeby referring to the flowchart shown in FIG. 11. In addition, at the stepS33, the controller 7 reflects the preparatorily decoded pictures and apreparatory decoding time, which are found in the process to findpreparatorily decoded pictures, in the edit-point table for each INpoint. Subsequently, the flow of the reproduction process goes on to astep S34. At the step S34, the controller 7 finds a decoding start timefor each of the edit points, which is described in the edit-point tableas an IN point, from the preparatory decoding time for the IN point, andreflects the decoding start time in the edit-point table. The decodingstart time of an IN point is a time at which a process to decode thepreparatorily decoded pictures for the IN time must be started.

[0274] It is to be noted that, basically, a decoding start time of anedit point serving as an IN point is set at a time leading ahead of theIN point by at least the preparatory decoding time for the IN point. Ifpicture B1 or B2 has been set at the edit point, however, a decodingstart time of the edit point is set at a time leading ahead of the editpoint by at least the sum of the preparatory decoding time for the editpoint and the decoding time of one frame.

[0275] The reason why the decoding time of one frame is added to thepreparatory decoding time as described above is explained as follows.Assume that picture B1 or B2 pertaining to GOP (n) is to be decoded. Inthis case, it is necessary to reference picture P15 pertaining to GOP(n−1) immediately preceding GOP (n) in the display order and picture I3pertaining to GOP (n). Picture I3 pertaining to GOP (n) is to bedisplayed after picture B1 and B2. Picture P15 pertaining to GOP (n−1)and picture I3 pertaining to GOP (n) are each called a referencedpicture for picture B1 or B2 pertaining to GOP (n), but only picture P15pertaining to GOP (n−1) immediately preceding GOP (n) in the displayorder is regarded as one of the preparatorily decoded pictures becausepicture P15 is not to be displayed after picture B1 or B2 pertaining toGOP (n). Since picture I3 pertaining to GOP (n) is to be displayed afterpicture B1 or B2 pertaining to the same group, however, picture I3 isnot regarded as one of the preparatorily decoded pictures.

[0276] Because picture I3 pertaining to GOP (n) is referenced indecoding picture B1 or B2 pertaining to GOP (n), nevertheless, it isnecessary to decode picture I3 before decoding picture B1 or B2.

[0277] Thus, before decoding picture B1 or B2 pertaining to GOP (n), itis necessary to decode picture I3 pertaining to GOP (n) in addition tothe pictures referred to as the preparatorily decoded pictures. For thisreason, if picture B1 or B2 has been set at an edit point, a decodingstart time of the edit point is set at a time leading ahead of the editpoint by at least the sum of the preparatory decoding time it takes todecode the preparatorily decoded pictures for the edit point and thedecoding time of one frame, which is picture I3 pertaining to the samegroup as picture B1 or B2.

[0278] As is obvious from the above description, for each edit pointincluded on the edit-point list, a created edit-point table showspreparatorily decoded pictures, a preparatory decoding time and adecoding start time, which are associated with the edit point like forexample one shown in FIG. 18.

[0279] Thus, the pieces of processing carried out at the steps S32 toS34 described above correspond to the scheduling performed at the stepS2 of the flowchart shown in FIG. 6.

[0280] Then, at the next step S35, the controller 7 forms a judgment asto whether or not the decoders 4 ₁ to 4 _(k) have completed preparationsfor decoding operations. The judgment is formed repeatedly at the stepS35 till the preparations are completed. As the outcome of the judgmentformed at the step S35 indicates that the decoders 4 ₁ to 4 _(k) havecompleted the preparations for decoding operations, the flow of thereproduction process goes on to a step S36 at which the controller 7sets a variable n at an initial value of, for example, 1 and a variablem at an initial value of, for example, 1. The variable n is a variableidentifying a decoder 4 _(n), which is supposed to start a decodingoperation. On the other hand, the variable m is a variable identifying adecoder 4 _(m), which is supposed to be selected by the switcher 5.Subsequently, the flow of the reproduction process goes on to a stepS37.

[0281] At the step S37, the controller 7 drives the decoder 4, to starta decoding operation starting with a picture at which the first IN pointdescribed in the edit-point table has been set. In addition, thecontroller 7 controls the switcher 5 to select a decoding result outputby the decoder 4 _(m) and output the selected decoding result to thedisplay unit 6. Thus, a picture obtained as a result of a decodingoperation carried out by the decoder 4 _(m) is displayed on the displayunit 6.

[0282] Then, at the next step S38, the controller 7 forms a judgment asto whether or not the current timing is a timing for one of decodingstart points described in the edit-point table.

[0283] If the outcome of the judgment formed at the step S38 indicatesthat the current timing is not a timing for one of decoding start pointsdescribed in the edit-point table, the flow of the reproduction processgoes on to a step S43, skipping steps S39 to S42.

[0284] If the outcome of the judgment formed at the step S38 indicatesthat the current timing is a timing for one of decoding start pointsdescribed in the edit-point table, on the other hand, the flow of thereproduction process goes on to the step S39 at which the controller 7increments the variable n by typically 1. Then, the flow of thereproduction process goes on to a step S40.

[0285] A decoding start point judged at the step S38 to coincide withthe current timing is appropriately referred to hereafter as an observeddecoding start point.

[0286] At the step S40, the controller 7 forms a judgment as to whetheror not the variable n is greater than the decoder count K of thecounters 4 ₁ to 4 _(k). If the outcome of the judgment formed at thestep S40 indicates that the variable n is greater than the decoder countK, the flow of the reproduction process goes on to a step S41 at whichthe controller 7 initializes the variable n to a value of 1. Then, theflow of the reproduction process goes on to a step S42.

[0287] If the outcome of the judgment formed at the step S40 indicatesthat the variable n is not greater than the decoder count K, on theother hand, the flow of the reproduction process goes on directly to thestep S42. At this step, the controller 7 drives the decoder 4 _(n) tostart an operation to decode preparatorily decoded pictures associatedwith the observed decoding start point described in the edit-pointtable. Then, the flow of the reproduction process goes on to the stepS43.

[0288] At the step S43, the controller 7 forms a judgment as to whetheror not a picture to be decoded by a currently operating decoder is anIN-point picture. A currently operating decoder is one of the decoders 4₁ to 4 _(k), which is currently carrying out a decoding operation. AnIN-point picture is a picture at which an edit point has been set as anIN point.

[0289] If the outcome of the judgment formed at the step S43 indicatesthat the picture to be decoded by a currently operating decoder is notan IN-point picture, the flow of the reproduction process goes on to astep S49, skipping steps S44 to S48.

[0290] If the outcome of the judgment formed at the step S43 indicatesthat the picture to be decoded by a currently operating decoder is anIN-point picture, on the other hand, the flow of the reproductionprocess goes on to the step S44 at which the controller 7 copies thevalue of the variable m to a variable m′ and increments the variable mby typically 1. The variable m is a variable identifying a currentlyoperating decoder 4 _(m), the decoding output of which is selected bythe switcher 5. Then, the flow of the reproduction process goes on to astep S45.

[0291] At the step 45, the controller 7 forms a judgment as to whetheror not the variable m is greater than the decoder count K of thecounters 4 ₁ to 4 _(k). If the outcome of the judgment formed at thestep S45 indicates that the variable m is greater than the decoder countK, the flow of the reproduction process goes on to a step S46 at whichthe controller 7 initializes the variable m to a value of 1. Then, theflow of the reproduction process goes on to a step step 47.

[0292] If the outcome of the judgment formed at the step S45 indicatesthat the variable m is not greater than the decoder count K, on theother hand, the flow of the reproduction process goes on directly to thestep step 47. At this step, the controller 7 controls the switcher 5 toselect a decoding result output by the decoder 4 _(m) identified by thevariable m, which was incremented by 1 at the step S44 or initialized to1 at the step S46.

[0293] As a result, the screen appearing on the display unit 6 isswitched from a previous decoded picture to a new decoded picture. Theprevious decoded picture is a picture obtained as a result of a decodingoperation carried out by the decoder 4 _(m)′ identified by the variablem′, which is equal to the variable m before being incremented by 1 atthe step S44 and, of course, before being initialized to 1 at the stepS46. On the other hand, the new decoded picture is a picture obtained asa result of a decoding operation carried out by the decoder 4 _(m)identified by the variable m, which has been incremented by 1 at thestep S44 or, has been incremented by 1 at the step S44 and theninitialized to 1 at the step S46.

[0294] Subsequently, at the next step S48, the controller 7 stops thedecoding operation carried out by the decoder 4 _(m)′ identified by thevariable m′, which is equal to the variable m before being incrementedby 1 at the step S44 and, of course, before being initialized to 1 atthe step S46 as described above. Then, the flow of the reproductionprocess goes on to the step S49.

[0295] The pieces of processing carried out at the steps S35 to S48described above correspond to the control of the decoding unit 4 and theswitcher 5. This control is executed at the step S3 of the flowchartshown in FIG. 6.

[0296] At the step S49, the controller 7 forms a judgment as to whetheror not the user has operated the operation unit 8 to stop thereproduction process much like the step S4 of the flowchart shown inFIG. 6. If the outcome of the judgment formed at the step S49 indicatesthat the user has operated the operation unit 8 to stop the reproductionprocess, that is, if the controller 7 has received an operation signalto stop the reproduction process from the operation unit 8, theexecution of the reproduction process is ended. The operation signal tostop the reproduction process is properly referred to hereafter as areproduction stop operation signal.

[0297] If the outcome of the judgment formed at the step S49 indicatesthat the user has not operated the operation unit 8 to stop thereproduction process, on the other hand, the flow of the reproductionprocess goes on to a step S50 at which the controller 7 forms a judgmentas to whether or not the process to reproduce an editing result of theMPEG stream in accordance with the edit-point list read out at the stepS31 has been completed much like the step S5 of the flowchart shown inFIG. 6. If the outcome of the judgment formed at the step S50 indicatesthat the process to reproduce an editing result of the MPEG stream inaccordance with the edit-point list has not been completed, the flow ofthe reproduction process goes back to the step S38 to repeat the sameprocessing. If the outcome of the judgment formed at the step S50indicates that the process to reproduce an editing result of the MPEGstream in accordance with the edit-point list has been completed, on theother hand, the execution of the reproduction process is ended.

[0298] In accordance with the reproduction process represented by theflowchart shown in FIG. 17, decoding operations are carried out in thedecoders 4 ₁ to 4 _(k) in a decoding order of decoders 4 ₁, 4 ₂, —, 4_(k), 4 ₁, 4 ₂ and so on, and the switcher 5 is controlled to select apicture obtained as a result of a decoding operation. It is to be noted,however, that the order of decoders to carry out decoding operations andthe order of decoders selected by the switcher 5 are not limited tothose indicated by the flowchart.

[0299] As described above by referring to the flowchart shown in FIG.17, in the disc system shown in FIG. 12, the controller 7 reads out theedit-point list from the optical disc 1 and makes an edit-point tablefrom the edit-point list. Since the controller 7 controls the decoders 4₁ to 4 _(k) to carry out decoding operations of the MPEG stream on thebasis of information included in the edit-point table, the informationincluded in the edit-point table can be said to be decoding controlinformation for controlling the decoding operations.

[0300] The disc system shown in FIG. 12 is capable of making a decodingcontrol list described in accordance with a predetermined format fromthe decoding control information. In addition, if such a decodingcontrol list already exists, the disc system shown in FIG. 12 is capableof controlling the decoders 4 ₁ to 4 _(k) to carry out decodingoperations of the MPEG stream on the basis of the decoding control list.

[0301] Thus, the disc system shown in FIG. 12 has the function of areproduction apparatus for reproducing information from the optical disc1 in accordance with an edit-point list. In addition, the disc systemshown in FIG. 12 also has the function of a list-making apparatus formaking a decoding control list from the edit-point list and the functionof a reproduction apparatus for reproducing information from the opticaldisc 1 in accordance with the decoding control list. It is to be notedthat, for an operation to reproduce information from the optical disc 1in accordance with the decoding control list, the disc system shown inFIG. 12 is capable of reproducing information from the optical disc 1 inaccordance with the decoding control list, which is typically stored inadvance in the controller 7. As an alternative, the decoding controllist is recorded onto the optical disc 1 and, in an operation toreproduce information from the optical disc 1 in accordance with thedecoding control list, the decoding control list is first retrieved fromthe optical disc 1.

[0302] The following description explains functions of the disc systemshown in FIG. 12 with the disc system working as a list-making apparatusfor making a decoding control list as well as a reproduction apparatusfor reproducing information from the optical disc 1 in accordance withthe decoding control list. The list-making apparatus is virtually aninformation-processing apparatus for making a decoding control list. Itis to be noted that some of the blocks of the disc system shown in FIG.12 carry out the same operations as those described above. Thus, theexplanation of such blocks does not need to be repeated.

[0303] The description begins with an explanation of a function executedby the disc system of FIG. 12 as a list-making apparatus for making adecoding control list. It is to be noted that the optical disc 1 shownin FIG. 12 is assumed to be a disc for recording an MPEG stream obtainedtypically as a result of carrying out an MPEG encoding process on amoving picture. In addition, the optical disc 1 is also used for storingan edit-point list made as a result of carrying out an editing processwith an MPEG stream in the optical disc 1 used as a raw editingmaterial.

[0304] The controller 7 makes an edit-point list as requested forexample by an operation signal generated by the operation unit 8. To putit in detail, when the controller 7 receives an operation signalrequesting creation of an edit-point list from the operation unit 8, forexample, the controller 7 issues a request for the edit-point list tothe disc drive 2. At this request, the disc drive 2 reads out theedit-point list from the optical disc 1 and then outputs the list to thebus 3. Subsequently, the controller 7 receives the edit-point list andthen detects edit points from the list. In addition, for each of theedit points detected from the edit-point list, fewest possible picturesare detected. The one or fewest possible pictures are pictures that mustbe decoded first in order to decode pictures to be displayed at andafter the edit point, even though the one or fewest possible picturesthemselves are not to be displayed. The controller 7 then finds adecoding start point representing a timing with which an operation todecode the one or fewest possible pictures is started.

[0305] The controller 7 further makes a decoding control list describingdecoding control information. The decoding control information includeseach of edit points detected from the edit-point list and additionaldata associated with each of the edit points. The additional dataincludes the number of pictures, which are not to be displayed but mustbe decoded first in order to decode pictures to be displayed at andafter the edit point, and a decoding start point representing a timingto start an operation to decode the pictures, which are not to bedisplayed but must be decoded. The controller 7 then supplies thedecoding control list to the disc drive 2, onto which the list is to bestored, by way of the bus 3. It is to be noted that details of thedecoding control list will be explained later by referring to FIG. 22.

[0306] By referring to a flowchart shown in FIG. 19, the followingdescription explains a decoding control list creation process carriedout by the disc system shown in FIG. 12 to make a decoding control list.

[0307] When the user operates the operation unit 8 to make a decodingcontrol list from an edit-point list, the operation unit 8 supplies adecoding control list operation signal to the controller 7. The decodingcontrol list operation signal is an operation signal requesting thecontroller 7 to make a decoding control list.

[0308] When receiving the decoding control list operation signal fromthe operation unit 8 at a step S61, the controller 7 issues a requestfor an edit-point list to the disc drive 2. At this request, the discdrive 2 reads out the edit-point list from the optical disc 1 and thenoutputs the list to the bus 3. Subsequently, the controller 7 receivesthe edit-point list from the bus 3. Then, at the next step S62, thecontroller detects all edit points described on the edit-point list asIN and OUT points. Subsequently, for each of the detected edit points,the controller 7 finds fewest possible pictures and a decoding startpoint representing a timing with which an operation to decode the one orfewest possible pictures is started. As described earlier, the one orfewest possible pictures are pictures that must be decoded first inorder to decode pictures to be displayed at and after the edit pointeven though the one or fewest possible pictures themselves are not to bedisplayed. The controller 7 further makes a decoding control list basedon information such as the detected edit points, the number of fewestpossible pictures, which are not to be displayed but must be decoded foreach of the edit points, and the computed decoding start point for eachof the edit points. That is to say, the controller 7 makes a decodingcontrol list showing decoding control information including the detectededit points, the number of fewest possible pictures, which are not to bedisplayed but to be decoded for each of the edit points, and thecomputed decoding start point for each of the edit points.

[0309] Then, the flow of the list creation process goes on from the stepS62 to a step S63 at which the controller 7 outputs the decoding controllist made at the step S62 to the bus 3. The disc drive 2 receives thedecoding control list from the bus 3 and then stores the list onto theoptical disc 1 to end the execution of the list creation process.

[0310] As described above, in the decoding control list creation processrepresented by the flowchart shown in FIG. 19, the disc system shown inFIG. 12 is capable of making a decoding control list based on anedit-point list recorded on the optical disc 1 and storing the decodingcontrol list onto the optical disc 1. By carrying out a reproductionprocess to be described later with reference to a flowchart shown inFIG. 23, from the optical disc 1, the disc system shown in FIG. 12 oranother apparatus including a plurality of decoders is capable ofreproducing an MPEG stream including a decoding control list alsorecorded on the disc 1.

[0311] By referring to FIGS. 20 to 22, the following descriptionexplains the decoding control list made in the decoding control listcreation process represented by the flowchart shown in FIG. 19.

[0312] Now, assume that an editing operation like one shown in FIG. 20has been carried out.

[0313] An MPEG-stream portion between an IN point set on an MPEG streamused as a raw editing material and an OUT point for the IN point isreferred to as a clip. If a cut editing operation is carried out, theresult of the cut editing operation is a sequence of a plurality ofclips.

[0314] The upper portion of FIG. 20 shows a result of a cut editingoperation carried out on raw material data including 2 MPEG streams 301and 302.

[0315] In FIG. 20, the file names of the MPEG streams 301 and 302 are../0001/video01.mpg and ../0002/video02.mpg respectively. It is to benoted that, strictly speaking, ../0001/of the file name../0001/video01.mpg is the name of a directory or a folder including afile containing the MPEG stream 301, and video01.mpg is the name of thefile. ‘../’ represents a directory at a level immediately above thecurrent directory. This file naming applies to ../0002/video02.mpg aswell.

[0316] As shown in FIG. 20, a pair of IN and OUT points is set on theMPEG stream 301 to result in clip #1 between the IN and OUT points. Bythe same token, a pair of IN and OUT points is set on the MPEG stream302 to result in clip #2 between the IN and OUT points. Thus, clip #1 isa portion of the file ../0001/video01.mpg and clip #2 is a portion ofthe file ../0002/video02.mpg.

[0317] The so-called time code TC is attached to each of framescomposing the MPEG streams 301 and 302. Used for representing thedisplay timing of a frame to which the time code is attached, the timecode TC has a format of ‘Hours:Minutes:Seconds:Frame number’. Each editpoint set as an IN or OUT point is represented by a time code.

[0318] In FIG. 20, the IN point of clip #1 is represented by a TC of00:00:00:00 while the OUT point of clip #1 is represented by a TC of00:05:00:12. On the other hand, the IN point of clip #2 is representedby a TC of 00:10:00:03 while the OUT point of clip #2 is represented bya TC of 00:15:00:00.

[0319] Assume that an editing process was carried out to reproduce clip#1 to be followed by clip #2. As shown in displayed frames 303 of FIG.20, an edit point has been set as an OUT point at picture A7 pertainingto GOP (m) of clip #1 on the MPEG stream 301 and as an IN point atpicture C4 pertaining to GOP (m) of clip #2 on the MPEG stream 302. Inthis case, in an operation to reproduce the post-editing MPEG streams,as shown in output frames 304 of FIG. 20, the decoders 4 ₁ is driven todecode and output pictures ending with picture A7 at which an edit pointhas been set as the OUT point of clip #1 and, as shown in output frames305 of FIG. 20, the decoder 4 ₂ is driven to decode and output picturesstarting with picture C4 at which an edit point has been set as the INpoint of clip #2.

[0320] However, in order for the decoder 4 ₂ to decode frames startingwith frame C4 at which an edit point has been set as an IN point,specific pictures to be referenced in decoding the frames even thoughnot to be displayed must be decoded first prior to an operation todecode the frame C4 at which an edit point has been set as an IN point.As described earlier, such specific pictures are referred to aspreparatorily decoded pictures. As shown in the displayed frames 305 ofFIG. 20, four pictures C0, C1, C2 and C3 are the preparatorily decodedpictures of frame C4 and must thus be decoded prior to an operation todecode the frame C4. Since the IN point of clip #2 is represented by a‘TC=00:10 00:03’, the decoding start point of clip #2 is a picturerepresented by a ‘TC=00:10:59:29’, which is leading ahead of ‘TC=0010:00:03’ by a period of time it takes to decode four pictures.

[0321]FIG. 21 is a diagram showing a typical edit-point list made as aresult of an editing operation explained by referring to FIG. 20. Theedit-point list shown in FIG. 21 can be prescribed in a definition usinga language such as the XML (extensible, Markup Language).

[0322] To be more specific, FIG. 21 shows typical codes in a rangespecified by a <body> tag placed on the first line of the edit-pointlist to serve as a start tag and a </body> tag placed on the eleventhline to serve as an end tag. It is to be noted that, in the definitionof the edit-point list shown in FIG. 21, a number placed at thebeginning or each line and a colon ‘:’ following the number are notcodes but merely added properly to make the description easy tounderstand. Lines and colons shown in FIGS. 22 and 24 are added for thesame purpose as those shown in FIG. 21.

[0323] The edit-point list shown in FIG. 21 is a list of time codes eachrepresenting an edit point set in a rawmaterial data in order toidentify a clip and a list of time codes each representing a timing toreproduce a clip represented by data following an edit point. Pieces ofinformation included on the list begin at a <par> tag placed on thesecond line and end at a </par> tag placed on the tenth line.

[0324] ‘<!—Clip1—>’ on the third line indicates that codes described onthe fourth and fifth lines are codes of clip #1. It is to be noted thata comment can be described between ‘<!—’ and ‘—>’.

[0325] On the fourth and fifth lines, codes ‘<refsrc=“../0001/video01.mpg” begin=“smpte=00:00:00:00”clipBegin=“smpte=00:00:00:00” clipEnd=“00:05:00:12” />’ are described.The code ‘<ref src=“../0001/video01.mpg”’ thereof indicates that the‘../0001/video01.mpg’ is the name of a file containing the MPEG streamof clip #1. The code ‘begin=“smpte 00:00:00:00”’ thereof indicates thatan operation to reproduce clip #1 begins at a time code TC of00:00:00:00 of data following the edit point. The code‘begin=“smpte=00:00:00:00”’ can be omitted. The code‘clipBegin=“smpte=00:00:00:00”’ thereof indicates that the IN point ofclip #1 is set at the time code TC of 00:00:00:00 of file../0001/video01.mpg. On the other hand, the code‘clipEnd=“smpte=00:05:00:12”’ thereof indicates that the OUT point ofclip #1 is set at the time code TC of 00:05:00:12 of file../0001/video0.1.mpg. It is to be noted that the code ‘smpte=’ indicatesthat information following this code is a time code conforming tostandards set by the SMPTE (Society of Motion Picture and TelevisionEngineers). It is also worth noting that the afore described format ofthe time code is no more than a typical format. In actuality, any otherformat can be adopted as long as the other format indicates timeinformation of an order in which pictures are displayed.

[0326] ‘<!—Clip2—>’ on the seventh line indicates that codes describedon the eighth and ninth lines are codes of clip #2.

[0327] On the eighth and ninth lines, codes ‘<refsrc=“../0002/video02.mpg” begin=“smpte=00:05:00:12”clipBegin=“smpte=00:10:00:03” clipEnd=“00:15:00:00” />’ are described.The code ‘<ref src=“../0002/video02.mpg”’ thereof indicates that the‘../0002/video02.mpg’ is the name of a file containing the MPEG streamof clip #2. The code ‘begin=“smpte=00:05:00:13”’ thereof indicates thatan operation to reproduce clip #2 begins at a time code TC=00:05:00:13of data following the edit point. This is because the MPEG stream ofclip #2 is reproduced after the MPEG stream of clip #1 as explainedearlier by referring to FIG. 20. Since the reproduction period of timefor the MPEG stream of clip #1 is ‘00:05:00:12’ between the time codeTC=00:00:00:00 of file ../0001/video01.mpg and the time codeTC=00:05:00:12 of file ../0001/video01.mpg as described on the fifthline, the operation to reproduce clip #2 begins at a time codeTC=00:05:00:13. The code ‘clipBegin=“smpte=00:10:00:03”’ thereofindicates that the IN point of clip #2 is set at the time codeTC=00:10:00:03 of file ../0002/video02.mpg. On the other hand, the code‘clipEnd=“smpte=00:15:00:00”’ thereof indicates that the OUT point ofclip #2 is set at the time code TC=00:15:00:00 of file../0002/video02.mpg.

[0328]FIG. 22 is a diagram showing a typical decoding control list madeby carrying out the process to make a decoding control list inaccordance with the flowchart shown in FIG. 19 from the edit-point listshown in FIG. 21. As described before, the edit-point list shown in FIG.21 is made as a result of an editing operation explained earlier byreferring to FIG. 20. It is to be noted that, much like the edit-pointlist shown in FIG. 21, the decoding control list shown in FIG. 22 can beprescribed in a definition using a language such as the XML.

[0329] The decoding control list shown in FIG. 22 is made by addingpreDecBegin and preDecDur to the edit-point list shown in FIG. 21.preDecBegin is attributive information representing a decoding startpoint, which is a point of time to start an operation to decode picturesnot to be displayed. On the other hand, preDecDur is attributiveinformation representing the number of I and P pictures, which must bedecoded first before decoding a picture at which an edit point has beenset as an IN point.

[0330] To put it concretely, a code of ‘preDecBegin=“smpte=00:09:59:29”’on the tenth line is information specifying that an operation to decodeclip #2 specified by codes described on the eighth and ninth lines isstarted at a time code TC=00:09:59:29 set for file ../0002/video02.mpg.A code of ‘preDecDur=“4”’ is information indicating that the number of Iand P pictures, which must be decoded first before decoding a picture tobe displayed at a TC of 00:10:00:03 is 4. In the decoding control listshown in FIG. 22, the picture to be displayed at a TC of 00:10:00:03 ispicture C4 shown in FIG. 20. On the other hand, the I and P pictures,which must be decoded first before decoding picture C4, are pictures C0to C3 shown in FIG. 20.

[0331] By starting the operation to decode the four pictures, namely, C0to C3 specified by preDecDur at the time code TC=00:09:59:29 specifiedby preDecBegin, the disc system shown in FIG. 12 is capable ofseamlessly reproducing C4, which is the first picture of clip #2 to bedisplayed when a TC of 00:10:00:03 is reached.

[0332] It is to be noted that the operation to decode the four pictures,which starts at the time code TC=00:09:59:29 specified by preDecBegin,is carried out by a decoder different from a decoder used so far forcarrying out an operation to decode clip #1 specified by codes describedon the fourth and fifth lines.

[0333] In the decoding control list shown in FIG. 20, preDecBegin isdescribed to specify a time code for file ../0002/video02.mpg containingclip #2. However, preDecBegin can also be described for specifyinganother time code such as a time code of post-editing data. In thiscase, preDecBegin is described as ‘TC=00:05:00:08’, which leads ahead of‘TC=00:05:00:12’ by a period of time it takes to decode four frames.

[0334] As described above, the disc system shown in FIG. 12 makes adecoding control list and then stores the list onto the optical disc 1also shown in FIG. 12.

[0335] The following description explains the disc system of FIG. 12,which functions as a reproduction apparatus reproducing an MPEG streamfrom the optical disc 1 in accordance with a decoding control list.

[0336] It is to be noted that the optical disc 1 shown in FIG. 12 isassumed to contain an MPEG stream obtained typically as a result ofcarrying out an MPEG encoding process on a moving picture and contain adecoding control list made from an edit-point list.

[0337] The controller 7 controls the disc drive 2, the decoding unit 4and the switcher 5 typically in accordance with operation signalsreceived from the operation unit 8. When receiving an operation signal,which requests an operation to reproduce an MPEG stream from the opticaldisc 1, from the operation unit 8, for example, the controller 7 issuesa request for a decoding control list to the disc drive 2. At thisrequest, the disc drive 2 reads out a decoding control list from theoptical disc 1 and then outputs the list to the bus 3. Then, thecontroller 7 receives the decoding control list from the bus 3.

[0338] Subsequently, the controller 7 controls the decoders 4 ₁ to 4_(k) in picture units to carry out operations to decode encoded data onthe basis of the decoding control list. To put it in detail, thecontroller 7 controls the decoders 4 ₁ to 4 _(k) in picture units tocarry out operations to decode an MPEG stream on the basis of editpoints described on the decoding control list as decoding controlinformation, the number of fewest possible pictures for each of the editpoints and a start point representing a timing to start an operation todecode the one or fewest possible pictures. As described before, the oneor fewest possible pictures are pictures to be decoded first beforedecoding the picture displayed at and after the edit point. However, theone or fewest possible pictures themselves are not to be displayed. Inaddition, the controller 7 also controls the switcher 5 on the basis ofthe decoding control list so that the switcher 5 correctly selects adecoded picture output by one of the decoders 4 ₁ to 4 _(k).

[0339] By referring to a flowchart shown in FIG. 23, the followingdescription explains a reproduction process carried out by the discsystem shown in FIG. 12 on the basis of a decoding control list such asthe one shown in FIG. 22.

[0340] When the user operates the operation unit 8 to start a process toreproduce a result of edit processing of an MPEG stream in accordancewith an edit-point list, the operation unit 8 outputs areproduction-start operation signal, which is an operation signal makinga request for a start of a reproduction process, to the controller 7.

[0341] When receiving an operation signal to start a reproductionprocess from the operation unit 8 at a step S71, the controller 7 issuesa request for a decoding control list to the disc drive 2. At thisrequest, the disc drive 2 reads out the decoding control list from theoptical disc 1 and then outputs the list to the bus 3. The controller 7then receives the decoding control list from the bus 3. Subsequently,the flow of the reproduction process goes on to a step S72.

[0342] At the step S72, the controller 7 forms a judgment as to whetheror not the decoders 4 ₁ to 4 _(k) have completed preparations fordecoding operations. If the preparations for decoding operations havenot been completed, the formation of the judgment at the step S72 isrepeated. The judgment is formed at this step repeatedly till theoutcome of the judgment indicates that the decoders 4 ₁ to 4 _(k) havecompleted the preparations for decoding operations. As the outcome ofthe judgment indicates that the decoders 4 ₁ to 4 _(k) have completedthe preparations for decoding operations, the flow of the reproductionprocess goes on to a step S73 at which the controller 7 sets a variablen at an initial value of, for example, 1 and a variable m at an initialvalue of, for example, 1. The variable n is a variable identifying adecoder 4 _(n), which is supposed to start a decoding operation. On theother hand, the variable m is a variable identifying a decoder 4 _(m),which is supposed to be selected by the switcher 5. Subsequently, theflow of the reproduction process goes on to a step S74.

[0343] At the step S74, the controller 7 drives the decoder 4 _(n) tostart a decoding operation starting with a picture at which an IN pointdescribed on the decoding control list has been set. The IN point isdescribed for the clip to be reproduced first. In addition, thecontroller 7 controls the switcher 5 to select a decoding result outputby the decoder 4 and output the selected decoding result to the displayunit 6. Thus, a picture obtained as a result of a decoding operationcarried out by the decoder 4 _(m) is displayed on the display unit 6.

[0344] Then, at the next step S75, the controller 7 forms a judgment asto whether or not the current timing is a timing for one of decodingstart points described on the decoding control list, that is, whether ornot the current timing is a timing for a time code specified bypreDecBegin.

[0345] If the outcome of the judgment formed at the step S75 indicatesthat the current timing is not a timing for one of decoding start pointsdescribed on the decoding control list, that is, the outcome indicatesthe current timing is not a timing for a time code specified bypreDecBegin, the flow of the reproduction process goes on to a step S80,skipping steps S76 to S79.

[0346] If the outcome of the judgment formed at the step S75 indicatesthat the current timing is a timing for one of decoding start pointsdescribed on the decoding control list, that is, the outcome indicatesthe current timing is a timing for a time code specified by preDecBegin,on the other hand, the flow of the reproduction process goes on to thestep S76 at which the controller 7 increments the variable n bytypically 1. Then, the flow of the reproduction process goes on to astep S77.

[0347] preDecBegin specifying a time code, whose timing is judged at thestep S75 to coincide with the current timing, is appropriately referredto hereafter as observed preDecBegin.

[0348] At the step S77, the controller 7 forms a judgment as to whetheror not the variable n is greater than the decoder count K of thecounters 4 ₁ to 4 _(k). If the outcome of the judgment formed at thestep S77 indicates that the variable n is greater than the decoder countK, the flow of the reproduction process goes on to a step S78 at whichthe controller 7 initializes the variable n to a value of 1. Then, theflow of the reproduction process goes on to a step S79.

[0349] If the outcome of the judgment formed at the step S77 indicatesthat the variable n is not greater than the decoder count K, on theother hand, the flow of the reproduction process goes on directly to thestep S79. At this step, the controller 7 drives the decoder 4 _(n) tostart an operation to decode preparatorily decoded pictures, the numberof which is specified by preDecDur described on the decoding controllist, being associated with observed preDecBegin. Then, the flow of thereproduction process goes on to a step S80.

[0350] At the step S80, the controller 7 forms a judgment as to whetheror not a picture to be decoded by a currently operating decoder is anIN-point picture. A currently operating decoder is one of the decoders 4₁ to 4 _(k), which is currently carrying out a decoding operation. AnIN-point picture is a picture at which an edit point has been set as anIN point, that is, a picture with the time code thereof specified by anyone of clipBegin codes on the decoding control list.

[0351] If the outcome of the judgment formed at the step S80 indicatesthat the picture to be decoded by a currently operating decoder is not apicture with the time code thereof specified by clipBegin, the flow ofthe reproduction process goes on to a step S86, skipping steps S81 toS85.

[0352] If the outcome of the judgment formed at the step S80 indicatesthat the picture to be decoded by a currently operating decoder is apicture with the time code thereof specified by clipBegin, on the otherhand, the flow of the reproduction process goes on to the step S81 atwhich the controller 7 copies the value of the variable m to a variablem′ and increments the variable m by typically 1. The variable m is avariable identifying a currently operating decoder 4 _(m), the decodingoutput of which is selected by the switcher 5. Then, the flow of thereproduction process goes on to a step S82.

[0353] At the step S82, the controller 7 forms a judgment as to whetheror not the variable m is greater than the decoder count K of thecounters 4 ₁ to 4 _(k). If the outcome of the judgment formed at thestep S82 indicates that the variable m is greater than the decoder countK, the flow of the reproduction process goes on to a step S83 at whichthe controller 7 initializes the variable m to a value of 1. Then, theflow of the reproduction process goes on to a step S84.

[0354] If the outcome of the judgment formed at the step S82 indicatesthat the variable m is not greater than the decoder count K, on theother hand, the flow of the reproduction process goes on directly to thestep S84. At this step, the controller 7 controls the switcher 5 toselect a decoding result output by the decoder 4 _(m) identified by thevariable m, which was incremented by 1 at the step S81 or initialized to1 at the step S83.

[0355] As a result, the screen appearing on the display unit 6 isswitched from a previous decoded picture to a new decoded picture. Theprevious decoded picture is a picture obtained as a result of a decodingoperation carried out by the decoder 4 _(m)′ identified by the variablem′, which is equal to the variable m before being incremented by 1 atthe step S81 and, of course, before being initialized to 1 at the stepS83. On the other hand, the new decoded picture is a picture obtained asa result of a decoding operation carried out by the decoder 4 _(m)identified by the variable m, which has been incremented by 1 at thestep S81 or, has been incremented by 1 at the step S81 and theninitialized to 1 at the step S83.

[0356] Subsequently, at the next step S85, the controller 7 stops thedecoding operation carried out by the decoder 4 _(m)′ identified by thevariable m′, which is equal to the variable m before being incrementedby 1 at the step S81 and, of course, before being initialized to 1 atthe step S83 as described above. Then, the flow of the reproductionprocess goes on to the step S86.

[0357] At the step S86, the controller 7 forms a judgment as to whetheror not the user has operated the operation unit 8 to stop thereproduction. If the outcome of the judgment formed at the step S86indicates that the user has operated the operation unit 8 to stop thereproduction process, that is, if the controller 7 has received anoperation signal to stop the reproduction process from the operationunit 8, the execution of the reproduction process is ended. Theoperation signal to stop the reproduction process is properly referredto hereafter as a reproduction stop operation signal.

[0358] If the outcome of the judgment formed at the step S86 indicatesthat the user has not operated the operation unit 8 to stop thereproduction process, on the other hand, the flow of the reproductionprocess goes on to a step S87 at which the controller 7 forms a judgmentas to whether or not the process to reproduce an editing result of theMPEG stream in accordance with the decoding control list read out at thestep S71 has been completed. If the outcome of the judgment formed atthe step S87 indicates that the process to reproduce an editing resultof the MPEG stream in accordance with the decoding control list has notbeen completed, the flow of the reproduction process goes back to thestep S75 to repeat the same processing. If the outcome of the judgmentformed at the step S87 indicates that the process to reproduce anediting result of the MPEG stream in accordance with the decodingcontrol list has been completed, on the other hand, the execution of thereproduction process is ended.

[0359] As described above, in accordance with the reproduction processrepresented by the flowchart shown in FIG. 23, the disc system shown inFIG. 12 is capable of reading out a decoding control list recorded onthe optical disc 1 and then reproducing an MPEG stream from the opticaldisc 1 in accordance with the decoding control list.

[0360] Thus, by carrying out the reproduction process represented by theflowchart shown in FIG. 23, the disc system shown in FIG. 12 is capableof reproducing an MPEG stream from the optical disc 1, on which adecoding control list has been recorded in a process to make thedecoding control list in accordance with the flowchart shown in FIG. 19.In addition, the disc system shown in FIG. 12 is capable of reproducingan MPEG stream from the optical disc 1, on which a decoding control listmade by another apparatus has been recorded by the other apparatus.

[0361] In accordance with the reproduction process represented by theflowchart shown in FIG. 23, the disc system shown in FIG. 12 is capablereproducing an MPEG stream from the optical disc 1 in accordance with adecoding control list provided that the decoding control list has beenstored in the optical disc 1 even if an edit-point list has not beenrecorded on the optical disc 1.

[0362]FIG. 24 is a diagram showing another typical decoding controllist.

[0363] The decoding control list shown in FIG. 24 is identical with thatshown in FIG. 22 except that, in the case of the decoding control listshown in FIG. 24, descriptions each specifying a decoder are added tothe list on the sixth and eleventh lines.

[0364] It is to be noted that, in the decoding control list shown inFIG. 24, a description of ‘decoder=“0”’ specifying a decoder indicatesthat a decoder 4 _(p) is a decoder for decoding clip #1 to which thedescription is added. The decoder 4 _(p) is one of the K decoders 4 ₁ to4 _(k) employed in the disc system shown in FIG. 12. By the same token,a description of ‘decoder=“1”’ specifying a decoder indicates that adecoder 4 _(q) is a decoder for decoding clip #2 to which thedescription is added. The decoder 4 _(q) is also one of the K decoders 4₁ to 4 _(k). In this case, p±q. In addition, p and q are each an integerin the range 1 to K.

[0365] To be more specific, the description of ‘decoder=“0”’ on thesixth line of the decoding control list shown in FIG. 24 specifies thatthe decoder 4 _(p) is a decoder for decoding clip #1 specified by codesdescribed on the fourth and fifth lines as a clip of file../0001/video01.mpg from a TC of 00:00:00:00 to a TC of 00:05:00:12.

[0366] On the other hand, the description of ‘decoder=“1”’ on theeleventh line of the decoding control list shown in FIG. 24 specifiesthat the decoder 4 _(q) is a decoder for decoding I and P pictures,which must be decoded first during a decoding period of time starting ata TC of 00:09:59:29 in order to decode a first picture of clip #2specified by codes described on the ninth and tenth lines as a clip offile ../0002/video02.mpg from a TC of 00:10:00:03 to a TC of 00:15:00:00so as to display the first picture at the TC of 00:10:00:03.

[0367] As described above, the decoding control list can be made as alist including informative descriptions each specifying a decoder. Inthis case, the controller 7 employed in the disc system shown in FIG. 12selects a decoder specified on the decoding control list and drives theselected decoder to decode an MPEG stream.

[0368] That is to say, in the reproduction process carried out inaccordance with the flowchart shown in FIG. 23 on the basis of adecoding control list specifying no decoders, the variable n identifyinga decoder 4 _(n) among the K decoders 4 ₁ to 4 _(k) as a decoder tocarry out a decoding operation and the variable m identifying a decoder4 _(m) among the K decoders 4 ₁ to 4 _(k) as a decoder to be selected bythe switcher 5 are set initially at 1 and then incremented sequentiallythereafter. In a reproduction process carried out on the basis of adecoding control list specifying decoders as shown in FIG. 24, on theother hand, the disc system shown in FIG. 12 recognizes a decoderspecified on the decoding control list and then drives the recognizeddecoder to start a decoding operation with a timing of a time codespecified by preDecBegin on the same list. Then, as a picture at a timecode specified by clipBegin becomes an object of decoding, a decodingresult output by the recognized decoder is selected.

[0369] By referring to a flowchart shown in FIG. 25, the followingdescription explains a reproduction process carried out by the discsystem shown in FIG. 12 to make a decoding control list like for examplethe one shown in FIG. 22 from an edit-point list stored in the opticaldisc 1 and reproduce an MPEG stream on the basis of the decoding controllist.

[0370] Steps S121 to S123 are executed for the same purpose asrespectively steps S61 to S63 of the flowchart shown in FIG. 19. Asdescribed earlier, at the steps S61 to S63, the disc system shown inFIG. 12 makes a decoding control list based on an edit-point list storedin the optical disc 1 and stores the decoding control list onto theoptical disc 1.

[0371] Steps S124 to S140 are executed for the same purpose asrespectively steps S71 to S87 of the flowchart shown in FIG. 23. Asdescribed earlier, at the steps S71 to S87, the disc system shown inFIG. 12 reads out the decoding control list from the optical disc 1, andreproduces an MPEG stream from the optical disc 1 on the basis of thedecoding control list.

[0372] It is to be noted that, by saving the decoding control list madeat the step S122 in the controller 7, for example, the pieces ofprocessing carried out at the steps S123 and S124 can be eliminated.

[0373] As described above, the series of the operations is carried outby the controller 7, which can be implemented by hardware or software.If a controller 7 implemented by software is used for carrying out theseries of operations described above, a program composing the softwareis installed into typically a general-purpose computer implementing thecontroller 7.

[0374]FIG. 26 is a diagram showing a typical configuration of anembodiment implementing a computer, into which a program composing thesoftware to be executed to carry out the series of operations describedabove is installed.

[0375] The program is installed in a hard disc 105 or stored in advancein a ROM 103. The hard disc 105 and the ROM 103 each serve as arecording medium embedded in the computer.

[0376] In order to install the program into the hard disc 105, theprogram is first temporarily or permanently stored in advance in aremovable recording medium 111 such as a flexible disc, a CD-ROM(Compact Disc Read Only Memory), an MO (Magneto Optical) disc, a DVD(Digital Versatile Disc), a magnetic disc or a semiconductor memory. Theprogram stored in the removable recording medium 111 can then bepresented to the user as package software. Then, the program isinstalled into the hard disc 105 employed in the computer from theremovable recording medium 111 described above.

[0377] It is to be noted that, as an alternative to the installation ofthe program from the removable recording medium 111, the program isdownloaded to the computer from a download source through a radiocommunication using an artificial satellite for digital satellitebroadcasting or by way of a wire communication means such as a LAN(Local Area Network) or the Internet. A communication unit 108 employedin the computer receives the program downloaded as such and then finallyinstalls the program into the embedded hard disc 105.

[0378] The computer also has an embedded CPU (Central Processing Unit)102. The CPU 102 is connected to an input/output interface 110 by usinga bus 101. The user enters a command to the computer by operating one ofa keyboard, a mouse, a mike and another input means, which compose aninput unit 107. The input unit 107 then passes on the command to the CPU102 by way of the input/output interface 110. The program stored inadvance in the ROM (Read Only Memory) 103 is executed in accordance withthe command. Instead of being stored in the ROM 103, the program to beexecuted is installed in the hard disc 105 as described above. In thiscase, the program is loaded into a RAM 104 from the hard disc 105. Asexplained before, the program has been installed in the hard disc 105from a removable recording medium 111 mounted on a drive 109 or from adownload source by way of a satellite or a network to be received by thecommunication unit 108. By execution of the program, the CPU 102 carriesout the processes according to the flowcharts described above in any ofthe configurations shown in the block diagrams explained earlier. Then,if necessary, the CPU 102 typically outputs results of the processes toan output unit 106 including an LCD (Liquid Crystal Display), a speakerand other components by way of the input/output interface 110, transmitsthe results to the satellite or the network by way of the communicationunit 108 or records the results onto the hard disc 105.

[0379] In this specification, processing steps prescribing the programto be executed by the computer to implement a variety of operations donot necessarily have to be carried out sequentially along the time axisin accordance with a predetermined order represented by a flowchart.Instead, the steps may include operations to be carried out concurrentlyor individually.

[0380] In addition, the program can be executed by using a computer or aplurality of computers in a distributed processing system. Furthermore,the program can also be transmitted to a remote computer for execution.

[0381] As described above, the embodiments reproduce an edited MPEGstream. It is to be noted, however, that the present invention can alsobe applied to reproduction of encoded data other than an MPEG stream. Anexample of such encoded data is data obtained as a result of apredictive encoding process carried out by referring to other pictures.

[0382] In addition, in the embodiments, an edit-point list is recordedon the optical disc 1 in advance and the controller 7 acquires theedit-point list from the optical disc 1. However, the edit-point listcan also for example be recorded in a recording medium other than theoptical disc 1 or acquired from transmission media such as the Internet.The decoding control list can be acquired in the same way as theedit-point list.

[0383] Furthermore, in the embodiments, a GOP is a sequence of picturesB1, B2, I3, B4, B5, P6, B7, B8, P9, B10, B11, P12, B13, B14, P15.However, the present invention can also be applied to a GOP of adifferent sequence of pictures. For example, the present invention canbe applied to a GOP including no B and/or P pictures. Moreover, thepresent invention can also be applied to a closed or open GOP.

[0384] It is to be noted that, if the GOP is a GOP of a differentsequence of pictures, preparatorily decoded pictures will be differentfrom those found by carrying out the process represented by theflowchart shown in FIG. 11.

[0385] In addition, in the embodiments, the optical disc 1 is arecording medium for storing an MPEG stream to be reproduced. However,the present invention can also be applied to reproduction of an MPEGstream from a recording medium other than the optical disc 1. Examplesof the other recording medium are a magnetic disc, a magnetic tape and asemiconductor memory. The present invention can also be applied toreproduction of an MPEG stream downloaded from transmission media suchas the Internet or a satellite.

[0386] As described above, FIGS. 8 and 13 to 15 each show an examplewith picture B1 always taken as a picture at which an edit point is setas an IN point. As explained earlier by referring to FIG. 11, however, acase in which an edit point is set at picture B1 or B2 is a case havinga largest number of preparatorily decoded pictures. Thus, if a seamlessreproduction process can be carried out with an edit point set atpicture B1 or B2, naturally, a seamless reproduction process can also becarried out with an edit point set at a picture other than picture B1 orB2.

[0387] Furthermore, in the embodiments, the controller 7 detects editpoints set on an MPEG stream from an edit-point list. However, the useris also allowed to supply an edit point set on an MPEG stream to thecontroller 7 by, for example, operating the operation unit 8. As anotheralternative, an external means is used for detecting an edit point seton an MPEG stream and supplying the edit point to the controller 7. Thatis to say, there is specially no restriction on the method to supply anedit point set on an MPEG stream to the controller 7.

[0388] Moreover, in the embodiments, the same apparatus functions as anapparatus for making a decoding control list from an edit-point list andan apparatus for executing decoding control based on the decodingcontrol list. However, the present invention is not limited to thisscheme. For example, the apparatus for making a decoding control listfrom an edit-point list can be an apparatus different from the apparatusfor executing decoding control based on the decoding control list.

[0389] The present invention is not limited to the details of the abovedescribed preferred embodiments. The scope of the invention is definedby the appended claims and all changes and modifications as fall withinthe equivalence of the scope of the claims are therefore to be embracedby the invention.

What is claimed is:
 1. A decoding control apparatus for controlling aprocess to decode encoded data obtained as a result of a predictiveencoding process, said decoding control apparatus comprising: a picturedetector for determining one or fewest possible pictures, which must bedecoded first before decoding a picture to be displayed after an editpoint set in said encoded data but are not to be displayed; astart-point finder for finding a start point representing a timing tostart a process to decode said one or fewest possible picturesdetermined by said picture detector even though said one or fewestpossible pictures are not to be displayed; a decoding controller forcontrolling processes, which are carried out by a plurality of decodersfor decoding said encoded data in order to decode said encoded dat_(a),in picture units, on the basis of said start point; and a selector forselecting one of pictures, which are obtained as results of saidprocesses carried out by said decoders, on the basis of said edit pointand for outputting said selected picture.
 2. The decoding controlapparatus according to claim 1, further comprising an edit-pointdetector for detecting said edit point set in said encoded data.
 3. Thedecoding control apparatus according to claim 1, wherein said decodersare employed in said decoding control apparatus.
 4. The decoding controlapparatus according to claim 1, wherein, if said encoded data is encodedat an L-time decoding speed, where L is a positive number, the number ofsaid decoders is at least 7/L.
 5. The decoding control apparatusaccording to claim 1, wherein said start-point finder determines atiming leading ahead of a timing to start a process to decode a pictureat said edit point by at least a period of time it takes to decode allof said one or fewest possible pictures, which are determined by saidpicture detector, for said edit point, as pictures not to be displayed,as said start point.
 6. The decoding control apparatus according toclaim 1, wherein said encoded data is data generated by encodingpictures in unit of a group including a plurality of pictures.
 7. Thedecoding control apparatus according to claim 1, wherein: each of saidpictures include: an Intra (I) picture encoded without referencing otherpictures; a Predictive (P) picture encoded by referencing a picturedisplayed previously; or a Bidirectionally predictive (B) pictureencoded by referencing both a picture displayed previously and a pictureto be displayed later, or by referencing either of the picture displayedpreviously or the picture to be displayed later; said one or fewestpossible pictures, which are identified by said picture detector but notto be displayed, are I or P pictures.
 8. The decoding control apparatusaccording to claim 1, wherein said decoding controller: drives one ofsaid decoders, which is currently not carrying out a decoding process,to start a process to decode said encoded data with a timing of a newstart point; and drives said one of decoders, which has been carryingout said process to decode said encoded data by starting said processwith said timing of said new start point, to stop said process to decodesaid encoded data with a timing of an edit point appearing next to saidnew start point.
 9. The decoding control apparatus according to claim 8,wherein with said timing of an edit point appearing next to said newstart point, said selector starts selecting pictures obtained as aresult of said decoding process carried out by said one of saiddecoders, which has been carrying out said decoding process by startingsaid decoding process with said timing of said new start point.
 10. Thedecoding control apparatus according to claim 1, said decoding controlapparatus further comprising a reader for reading out said encoded datafrom a recording medium, on which said encoded data has been stored. 11.A decoding control method for controlling a process to decode encodeddata obtained as a result of a predictive encoding process, saiddecoding control method comprising the steps of: determining one orfewest possible pictures, which must be decoded first before decoding apicture to be displayed after an edit point set in said encoded data butare not to be displayed; finding a start point representing a timing tostart a process to decode said one or fewest possible pictures eventhough said one or fewest possible pictures are not to be displayed;controlling processes, which are carried out by a plurality of decodersfor decoding said encoded data in order to decode said encoded dat_(a),in picture units, on the basis of said start point; and selecting one ofpictures, which are obtained as results of said processes carried out bysaid decoders, on the basis of said edit point.
 12. The decoding controlmethod according to claim 11, further comprising the step of detectingsaid edit point set in said encoded data.
 13. The decoding controlmethod according to claim 11 whereby, at said step of finding a startpoint, an operation is carried out to determine a timing leading aheadof a timing to start a process to decode a picture at said edit point byat least a period of time it takes to decode all of said one or fewestpossible pictures, which are determined by said picture detector, forsaid edit point, as pictures not to be displayed, as said start point.14. The decoding control method according to claim 11 whereby, at saidstep of controlling processes, one of said decoders, which is currentlynot carrying out a decoding process, is driven to start a process todecode said encoded data with a timing of a new start point; and saidone of decoders, which has been carrying out said process to decode saidencoded data by starting said process with said timing of said new startpoint, is driven to stop said process to decode said encoded data with atiming of an edit point appearing next to said new start point.
 15. Thedecoding control method according to claim 14 whereby, with said timingof an edit point appearing next to said new start point, at said step ofselecting one of pictures, an operation is started to select picturesobtained as a result of said decoding process carried out by said one ofdecoders, which has been carrying out said decoding process by startingsaid decoding process with said timing of said new start point.
 16. Thedecoding control method according to claim 11, said decoding controlmethod further comprising the step of reading out said encoded data froma recording medium, on which said encoded data has been stored.
 17. Aprogram for driving a computer to carry out a decoding control processto control a process of decoding encoded data obtained as a result of apredictive encoding process wherein said decoding control processcomprises the steps of: determining one or fewest possible pictures,which must be decoded first before decoding a picture to be displayedafter an edit point set in said encoded data but are not to bedisplayed; finding a start point representing a timing to start aprocess to decode said one or fewest possible pictures even though saidone or fewest possible pictures are not to be displayed; controllingprocesses, which are carried out by a plurality of decoders for decodingsaid encoded data in order to decode said encoded dat_(a), in pictureunits, on the basis of said start point; and selecting one of pictures,which are obtained as results of said processes carried out by saiddecoders, on the basis of said edit point.
 18. The program according toclaim 17, wherein said decoding control process further comprises thestep of detecting said edit point set in said encoded data.
 19. Theprogram according to claim 17, wherein at said step of finding a startpoint, an operation is carried out to determine a timing leading aheadof a timing to start a process to decode a picture at said edit point byat least a period of time it takes to decode all of said one or fewestpossible pictures, which are determined by said picture detector, forsaid edit point, as pictures not to be displayed, as said start point.20. The program according to claim 17, wherein at said step ofcontrolling processes, one of said decoders, which is currently notcarrying out a decoding process, is driven to start a process to decodesaid encoded data with a timing of a new start point; and said one ofdecoders, which has been carrying out said process to decode saidencoded data by starting said process with said timing of said new startpoint, is driven to stop said process to decode said encoded data with atiming of an edit point appearing next to said new start point.
 21. Theprogram according to claim 20, wherein with said timing of an edit pointappearing next to said new start point, at said step of selecting one ofpictures, an operation is started to select pictures obtained as aresult of said decoding process carried out by said one of decoders,which has been carrying out said decoding process by starting saiddecoding process with said timing of said new start point.
 22. Theprogram according to claim 17 wherein said decoding control processfurther comprises the step of reading out said encoded data from arecording medium, on which said encoded data has been stored.
 23. Aninformation-processing apparatus comprising: a picture detector fordetermining one or fewest possible pictures, which are not to bedisplayed but must be decoded first before decoding a picture to bedisplayed after an edit point described on an edit-point list, that is,a list of said edit point set in encoded data obtained as a result of apredictive encoding process; a start-point finder for finding a startpoint representing a timing to start a process to decode said one orfewest possible pictures determined by said picture detector even thoughsaid one or fewest possible pictures are not to be displayed; and adecoding control list maker for making a decoding control listdescribing at least said edit point and said start point as decodingcontrol information for controlling processes carried out by a pluralityof decoders for decoding said encoded data in order to decode saidencoded data.
 24. The information-processing apparatus according toclaim 23, further comprising an edit-point detector for detecting saidedit point set in said encoded data.
 25. The information-processingapparatus according to claim 23, wherein said start-point finderdetermines a timing leading ahead of a timing to start a process todecode a picture at said edit point by at least a period of time ittakes to decode all of said one or fewest possible pictures, which aredetermined by said picture detector, for said edit point, as picturesnot to be displayed, as said start point.
 26. The information-processingapparatus according to claim 23, wherein said encoded data is datagenerated by encoding pictures in unit of a group including a pluralityof pictures.
 27. The information-processing apparatus according to claim23 wherein: each of said pictures include: an Intra (I) picture encodedwithout referencing other pictures; a Predictive (P) picture encoded byreferencing a picture displayed previously; or a Bidirectionallypredictive (B) picture encoded by referencing both a picture displayedpreviously and a picture to be displayed later, or by referencing eitherof the picture displayed previously or the picture to be displayedlater; said one or fewest possible pictures, which are identified bysaid picture detector but not to be displayed, are I or P pictures. 28.The information-processing apparatus according to claim 23, wherein saiddecoding control list made by said decoding control list maker includesinformation used for specifying one of said decoders to carry out aprocess to decode said encoded data beginning from said start point assaid decoding control information.
 29. An information-processing methodcomprising the steps of: detecting one or fewest possible pictures,which are not to be displayed but must be decoded first before decodinga picture to be displayed after an edit point described on an edit-pointlist, that is, a list of said edit point set in encoded data obtained asa result of a predictive encoding process; finding a start point eachrepresenting a timing to start a process to decode said one or fewestpossible pictures determined by said picture detector even though saidone or fewest possible pictures are not to be displayed; and making adecoding control list describing at least said edit point and said startpoint as decoding control information for controlling processes carriedout by a plurality of decoders for decoding said encoded data in orderto decode said encoded data.
 30. The information-processing methodaccording to claim 29, said information-processing method furthercomprising the step of detecting said edit point set in said encodeddata.
 31. The information-processing method according to claim 29whereby, at said step of finding a start point, an operation is carriedout to determine a timing leading ahead of a timing to start a processto decode a picture at said edit point by at least a period of time ittakes to decode all of said one or fewest possible pictures, which aredetermined by said picture detector, for said edit point, as picturesnot to be displayed, as said start point.
 32. The information-processingmethod according to claim 29, wherein said decoding control list made atsaid step of making a decoding control list includes information usedfor specifying one of said decoders to carry out a process to decodesaid encoded data beginning from said start point as said decodingcontrol information.
 33. A program for driving a computer to carry out apredetermined process, said program comprising the steps of: determiningone or fewest possible pictures, which are not to be displayed but mustbe decoded first before decoding a picture to be displayed after an editpoint described on an edit-point list, that is, a list of said editpoint set in encoded data obtained as a result of a predictive encodingprocess; finding a start point each representing a timing to start aprocess to decode said one or fewest possible pictures determined bysaid picture detector even though said one or fewest possible picturesare not to be displayed; and making a decoding control list describingat least said edit point and said start point as decoding controlinformation for controlling processes carried out by a plurality ofdecoders for decoding said encoded data in order to decode said encodeddata.
 34. The program according to claim 33, said program furthercomprising the step of detecting said edit point set in said encodeddata.
 35. The program according to claim 33, wherein at said step offinding a start point, an operation is carried out to determine a timingleading ahead of a timing to start a process to decode a picture at saidedit point by at least a period of time it takes to decode all of saidone or fewest possible pictures, which are determined by said picturedetector, for said edit point, as pictures not to be displayed, as saidstart point.
 36. The program according to claim 33, wherein saiddecoding control list made at said step of making a decoding controllist includes information used for specifying one of said decoders tocarry out a process to decode said encoded data beginning from saidstart point as said decoding control information.
 37. A decoding controlapparatus for controlling a process to decode encoded data obtained as aresult of a predictive encoding process, said decoding control apparatuscomprising: a decoding controller for controlling processes carried outby a plurality of decoders for decoding said encoded data in order todecode said encoded data in picture units on the basis of a decodingcontrol list describing at least an edit point set in said encoded dataand a start point representing a timing to start a process to decodefewest possible pictures, which are not to be displayed but must bedecoded first before decoding a picture to be displayed after said editpoint, as decoding control information for controlling said processescarried out by said decoders for decoding said encoded data in order todecode said encoded data; and a selector for selecting one of pictures,which are obtained as results of said processes carried out by saiddecoders, on the basis of said decoding control list and for outputtingsaid selected picture.
 38. The decoding control apparatus according toclaim 37 wherein said decoders are employed in said decoding controlapparatus.
 39. The decoding control apparatus according to claim 37,wherein if said encoded data is encoded at an L-time decoding speed,where L is a positive number, the number of said decoders is at least7/L.
 40. The decoding control apparatus according to claim 37, whereinsaid encoded data is data generated by encoding pictures in unit of agroup including a plurality of pictures.
 41. The decoding controlapparatus according to claim 37, wherein: each of said pictures include:an Intra (I) picture encoded without referencing other pictures; aPredictive (P) picture encoded by referencing a picture displayedpreviously; or a Bidirectionally predictive (B) picture encoded byreferencing both a picture displayed previously and a picture to bedisplayed later, or by referencing either of the picture displayedpreviously or the picture to be displayed later; said one or fewestpossible pictures, which are identified by said picture detector but notto be displayed, are I or P pictures.
 42. The decoding control apparatusaccording to claim 37, said decoding control apparatus furthercomprising a reader for reading out said encoded data from a recordingmedium, on which said encoded data has been stored.
 43. The decodingcontrol apparatus according to claim 37, wherein said decoding controllist includes information used for specifying one of said decoders tocarry out a process to decode said encoded data beginning from saidstart point as said decoding control information.
 44. A decoding controlmethod for controlling a process to decode encoded data obtained as aresult of a predictive encoding process, said decoding control methodcomprising the steps of: controlling processes carried out by aplurality of decoders for decoding said encoded data in order to decodesaid encoded data in picture units on the basis of a decoding controllist describing at least an edit point set in said encoded data and astart point representing a timing to start a process to decode fewestpossible pictures, which are not to be displayed but must be decodedfirst before decoding a picture to be displayed after said edit point asdecoding control information for controlling said processes carried outby said decoders for decoding said encoded data in order to decode saidencoded data; and selecting one of pictures, which are obtained asresults of said processes carried out by said decoders, on the basis ofsaid decoding control list and outputting said selected picture.
 45. Thedecoding control method according to claim 44, said decoding controlmethod further comprising the step of reading out said encoded data froma recording medium, on which said encoded data has been stored.
 46. Thedecoding control method according to claim 44, wherein said decodingcontrol list includes information used for specifying one of saiddecoders to carry out a process to decode said encoded data beginningfrom said start point as said decoding control information.
 47. Aprogram for driving a computer to carry out a decoding control processof decoding encoded data obtained as a result of a predictive encodingprocess wherein said decoding control process comprises the steps of:controlling processes carried out by a plurality of decoders fordecoding said encoded data in order to decode said encoded data inpicture units on the basis of a decoding control list describing atleast an edit point set in said encoded data and a start pointrepresenting a timing to start a process to decode fewest possiblepictures, which are not to be displayed but must be decoded first beforedecoding a picture to be displayed after said edit point as decodingcontrol information for controlling said processes carried out by saiddecoders for decoding said encoded data in order to decode said encodeddata; and selecting one of pictures, which are obtained as results ofsaid processes carried out by said decoders, on the basis of saiddecoding control list and outputting said selected picture.
 48. Theprogram according to claim 47, wherein said decoding control processfurther comprises the step of reading out said encoded data from arecording medium, on which said encoded data has been stored.
 49. Theprogram according to claim 47, wherein said decoding control listincludes information used for specifying one of said decoders to carryout a process to decode said encoded data beginning from said startpoint as said decoding control information.